Injection systems having an injection pump and separate in- jectors are known in which an external pump supplies the liq- uid fuel under pressure to the injectors (generally one per cylinder) through tubing, and each injector acts as a nozzle synchronized with the operating cycle for the admission of the fuel into the combustion chamber of the engine.

Traditionally, the injection pump is of the type having a plunger with regulation of the delivery. Of the various types, variable reflux pumps are based on a principle of regulation of the useful capacity, which consists in causing a portion of the fuel to flow back in the supply duct to the pump during the delivery stroke.

Of the variable reflux pumps, the Bosch pump is constituted by a number of pumping members equal to that of the engine cylinders. Each of those members comprises a small cylinder in which a plunger controlled by a camshaft is slidably ar- ranged.

The plunger has a helical groove on its surface. A pumping chamber is filled by an external fuel supply pump until the plunger, during its stroke, shuts off the supply opening, closing it. From that moment the fuel contained in the cham- ber is compressed until a non-return delivery valve opens and delivery takes place, this lasting until the helical groove of the plunger uncovers an outflow opening of the chamber through which the fuel can flow out of the chamber to the tank (reflux), thus causing the pressure to fall and the de- livery valve to close.

The instant of reflux, and therefore the delivery, is regu- lated by the angular position of the plunger, which is fixed by a rack controlled by an external regulating device, such as, for example, the accelerator. By rotating the plunger by means of the rack, the instant at which the helical groove uncovers the outflow opening is advanced or delayed, and therefore delivery is regulated.

As stated, the prior art lists injection pump configurations which perform the tasks of metering the fuel and pumping un- der pressure, but the control of which is separate from that of the nozzle proper.

Injector-pumps are also known in which the nozzle forms a single body with the injection pump because the closing mem- ber, in addition to performing the function of distribution, also acts as a reciprocating pump plunger. The injector-pump eliminates the long pump-injector feed ducts with the associ- ated disadvantages in terms of deformability of the ducts and multiple injections.

A known injection system having an injector-pump is the sys- tem of the Cummins type which comprises one or more valves for regulating the amount of fuel to be injected, which valves are arranged along the fuel supply path from the tank to the injector-pump and are controlled by an external regu- lating device, for example the accelerator pedal. The injec- tor-pump receives a pre-metered amount of fuel and the plunger increases the injection pressure forcing the fuel through the oriented holes of the nozzle. The open-type noz- zle used in the Cummins system permits the suction into the injector of an amount of air for pre-mixing the fuel before spraying into the combustion chamber of the engine cylinder, and it is therefore to be preferred in the development of in- jection systems for diesel cycle engines by virtue of the value of pre-mixed injection in terms of optimisation of com- bustion and the consequent smaller quantity of unburnt resi- dues, which influence the reduction of pollutants.

A disadvantage of the injector-pump according to the Cummins system is that the amount of fuel fed to the nozzle in order to be admitted at high pressure into the combustion chamber is metered along a path upstream of the injector-pump by means of pressure-regulating valves, which leads to an over- all bulky and expensive system.

The object of the present invention is to provide a further- improved injector-pump device which combines the advantages of the Cummins-type technology having an open nozzle with a less expensive and non-bulky simplified structure.

To that end, the present invention relates to an injector- pump device having the features claimed in claim 1.

Particular embodiments of the invention are described in the dependent claims.

In summary, the injector-pump device to which the invention relates and which is to be used both in single-cylinder en- gines and in multi-cylinder engines, is in the form of a sin- gle integrated body comprising the injector proper (or noz- zle), the injection pump and an associated control mechanism for metering the amount of fuel to be injected.

In a preferred embodiment in the version for a single- cylinder engine, the above-mentioned injection pump can also be arranged to operate as a device for the independent supply and the circulation of the fuel inside the entire apparatus.

That function is particularly advantageous if the device is installed in an engine provided with an attached fuel tank because it incorporates in a single body having compact di- mensions, devices that are normally produced in separate parts.

In cases of installation in multi-cylinder engines, the in- jector-pump according to the invention is preferably supplied by an external auxiliary supply pump but preserves the prop- erties of reduced bulk and a simplified structure.

The configuration of the injector-pump having the function of metering, pumping and atomizing provides a single shaped in- jector plunger including three interconnected consecutive cy- lindrical sections, preferably having a diameter decreasing towards the atomizer nozzle, in which the cylindrical section having the largest diameter performs the function of metering the fuel, the intermediate section performs the function of pumping, that is to say, the injecting function proper, and the section having the smallest diameter performs the func- tion of a mechanically controlled closing member in co- operation with an atomizer nozzle having open holes.

As stated above, when used for single-cylinder engines, the cylindrical section for metering the fuel also effects the suction of the fuel from the tank and the circulation thereof throughout the apparatus, by means of valves integrated in the actual body of the injector.

Advantageously, by integrating in a single device the three normally separate functions of an injection apparatus, that is to say, metering, pumping and injecting, the solution ac- cording to the invention brings clear benefits in terms of the elimination of accessories and connections there between, and reduction in space requirement.

Further features and advantages of the invention will emerge clearly from the following detailed description which is pro- vided by way of non-limiting example with reference to the appended drawings in which: Figure 1 is a partial longitudinal section through a first embodiment of the injector-pump device according to the in- vention; Figure 2 is a partial longitudinal section through a second embodiment of the injector-pump device according to the in- vention ; Figure 3 is a partial longitudinal section through a third embodiment of the injector-pump device according to the in- vention; Figures 4a and 4b show the injector-pump device according to the first embodiment in two operative configurations ; Figures 5a and 5b show the injector-pump device according to the second embodiment in two operative configurations ; and Figures 6a and 6b show the injector-pump device in the third embodiment in two operative configurations.

With reference to the drawings, the injector-pump device ac- cording to the invention is generally indicated 10.

It comprises a boby 12 constituted by a substantially cylin- drical monolithic principal portion 14 and by a likewise cy- lindrical terminal portion 20 which is axially centred with respect to the principal portion 14 and is permanently cou- pled thereto by means of a socket member 22.

An axial cavity 16 for accommodating a plunger 18 having sec- tions with different diameters is defined in the portions of the body 12 thus coupled. The cavity 16 for accommodating the plunger includes three cylindrical sections of decreasing di- ameter, each suitable for accommodating, in a sliding manner, a corresponding section of the plunger 18 and for defining a corresponding fuel-treatment chamber, as will be explained in detail in the further course of the present description.

The terminal portion 20 has at its end a nozzle formation 24 which is suitable for facing the inside of a combustion cham- ber and in which injection orifices 26 are defined.

The principal portion 14 of the body 12 is surmounted by a ring nut 28 which has a recess 30 forming a seat for one end of a return spring 32. The spring is in abutment at the oppo- site end inside an annular seat 34 of a small plate 36 con- strained on the head of the plunger 18. The small plate 36 is associated with a tappet to which the plunger is anchored and which is held by the spring in contact with an eccentric of the timing system of the engine, having a profile designed in such a manner as to effect the movement of the plunger in ac- cordance with a desired law.

The plunger 18 comprises three cylindrical sections of de- creasing diameter: a first metering section 40, a second pumping and injecting section 42 and a third atomiz- ing/closing section 44, respectively.

The metering section 40 has on its surface a longitudinal re- cess 50 which extends from the end for connection to the pumping and injecting section 42 as far as an upper annular recess 52. The longitudinal recess 50 is also connected in a central portion to a groove 54 which extends in a helical manner and which has the function of metering the amount of fuel which is transferable to the pumping and injecting sec- tions as a function of the angular position of the plunger, which is determined by the rotation thereof which is con- trolled, for example, by means of a collar 56 keyed onto the plunger 12 and provided with a drive device 58.

A first section 60 of the cavity 16-suitable for receiving the metering section 40 of the plunger in a sealed manner- is connected, by way of an annular admission opening 62, a passage 63 and an admission valve 64, to a fuel supply line (not shown) and, by way of an outflow opening 66 and an out- flow valve 68, to a line (not shown) for the outflow of the fuel, for example in order to return it to the tank.

An escape passage 69 is formed in the portion 14 of the in- jector-pump body, between the section 60 and the outflow opening 66, downstream of the valve 68.

A metering chamber 70 is defined between the metering section 40 of the plunger and the base of the section 60 of the axial cavity 16.

A second section 72 of the cavity 16, which section is suit- able for receiving the pumping and injecting section 42 of the plunger in a sealed manner, defines with that section a chamber 74 communicating with the chamber 70 by way of a pas- sage 76 which is formed in the thickness of the body 12 and which is closed off by a unidirectional valve 78 for control- ling the flow of fuel.

A third section 80 of the cavity 16, which section is formed in the terminal portion 24 of the body of the device, is suitable for receiving the closing section 44 of the plunger and defines therewith an atomizing chamber communicating with the combustion chamber by way of the injection orifices 26.

Figures 2 and 3 show, respectively, two variants of the de- vice according to the invention, which are particularly suit- able for a multi-cylinder engine, in which the function of supplying the fuel to the individual injector-pump devices of each cylinder is entrusted to an external supply pump.

The variant of Figure 2 does not have the valve 64 for the suction of the fuel, while the variant of Figure 3 is a fur- ther-simplified variant in which the outflow valve 68 has also been omitted.

Owing to those variants, the longitudinal recess 50 and the helical groove 54 of the metering section 40 of the plunger have a different form, while the annular recess 52 is merged with the helical groove. In particular, the longitudinal re- cess 50 extends over only the lower portion of the section 40 as far as the helical groove 54, to which the annular recess 52 is connected, and is connected to a recess 50'which has a partial circumferential extent and which is suitable for closing off the admission opening 62 in a start-of-stroke po- sition of the plunger 18.

The remaining members, which are identical to those already described in relation to the. embodiment of Figure 1, are identified by the same alphanumeric references.

The functioning of the injector-pump device according to the invention will be described hereinafter with reference to Figures 4a and 4b.

Figure 4a shows the device in a first operative condition in which the plunger 18 is in a start-of-stroke position in which the closing section is at a distance from the atomizer orifices owing to the action of the return spring 32 which urges the head of the plunger to follow the profile of the eccentric of the engine timing system.

The ascending movement of the plunger brings about the suc- tion of the liquid fuel into the metering cavity 60 through the admission valve 64, the opening 62 and the longitudinal recess 50. At the same time, the air present in the combus- tion chamber is forced, during the compression stroke, into the atomizing chamber 80 through the open orifices 26.

During a subsequent injection stage, the plunger is con- trolled in its downstroke by the engine timing system, against the return spring 32.

When the plunger descends, the fuel collected in the chamber 70 is transferred forcedly through the duct 76 and the valve 78 into the chamber 74 which is delimited at the top by the pumping and injecting section 42 of the plunger.

The amount of fuel transferred into the pumping and injecting section is determined by the metering section 40 of the plunger, and in particular by the rotation imparted to the plunger and the consequent position of the helical groove 54 thereof relative to the outflow opening 66 which the groove closes off during the downstroke of the plunger.

The rotation of the plunger varies the position of closing off the outflow opening on the part of the helical groove during the downstroke of the plunger, and by delaying or ad- vancing that instant the delivery is increased or decreased.

The fuel is transferred from the metering chamber 70 to the pumping and injecting chamber 74 as long as it cannot flow back through the longitudinal recess 50 and the helical groove 54 connected thereto and the outflow opening 66.

The connection between the unidirectional valve 78 and the pumping chamber 74 is effected at a level correlated with the operative characteristics of the helical groove 54 in such a manner that the descent of the pumping and injecting section 42 of the plunger permits the total covering thereof for any quantity of fuel only at the end of the metering stage and before the generation of the high pressure of the fuel which is admitted into the combustion chamber of the engine.

The fuel present in the pumping and injecting chamber 74 is simultaneously compressed by the descending movement of the section 42 of the plunger and transferred into the atomizing chamber 80 and towards the injection orifices 26, and, at the same time, it is premixed with the air introduced. The mix- ture is forced from the chamber 80 into the combustion cham- ber of the engine in whose cylinder head the injector-pump device is mounted, until the end-of-stroke position of the plunger 18, shown in Figure 4b, is reached, in which position the closing section closes the nozzle (remaining in that closed configuration in the course of the combustion and ex- haust stage).

At the same time, any fuel pocket or air present in the cav- ity 60 is expelled through the annular recess 52 which is in communication with the outflow line downstream of the valve 68.

Figures 5a, 5b and 6a, 6b show the start-of-stroke and end- of-stroke configurations, respectively, of the plunger 18 in- side the cavity for the variants described above. The control of the device, the regulation of the metering of the fuel and the injection thereof are effected by similar methods in each embodiment considered. In the end position, in which the at- omizing nozzle is closed, when injection has taken place, the circulation of the fuel is brought about between the supply line and the outflow line to the tank through the annular re- cess and the helical groove, in order to cool and deaerate the section.

Owing to the structural characteristics of the injector-pump to which the invention relates, the metering of the fuel, its transfer to the pumping and injecting chamber and its admis- sion into the atomizer take place simultaneously during the descent of the plunger.

Advantageously, the configuration of the plunger of the in- jector-pump device according to the invention, which is suit- able for the simultaneous performance of the functions of me- tering, pumping and injecting, confers on the injector-pump device a greater speed of operation, greater precision and greater functioning efficiency, enabling a higher injection pressure and less gas and noise pollution of the engine on which the device is mounted to be obtained.

Moreover, the device can advantageously be produced in geo- metrically regular contained forms and dimensions. This mini- mises its dimensions in the axial extent, which are smaller than those of the current devices on the market, being advan- tageous in terms of installation and the direct control thereof when accommodated in the cylinder head of an engine, for example a multi-valve engine.

The device is also composed of a smaller number of constitu- ent members compared with the known devices, with clear ad- vantages in terms of simplicity, functionality, reliability of operation and production costs.

The device described, while being based on a configuration of the atomizing section known in the art, nevertheless permits the provision of an injection and pump system which is free from external accessories, such as the regulating and meter- ing valves, and permits installation in single-cylinder and multi-cylinder engines, advantageously of small displacement, conferring on them the advantages of pre-mixed injection in terms of optimisation of combustion.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without thereby de- parting from the protective scope of the present invention defined by the appended claims.