PUMP UNIT FOR SUPPLYING FU EL, PREFERABLY DI ESEL OIL, FROM A CONTAINING TAN K TO AN INTERNAL COMBUSTION ENGIN E

The present invention relates to a pump unit for supplying fuel, preferably diesel oil, from a containing tank to an internal combustion engine.

In particular, the present invention relates to a pump unit of the type comprising a pre-feed pump, for example an electric pump, adapted to draw the fuel from a containing tank; a high-pressure pump, for example a piston pump, adapted to feed the fuel to an internal combustion engine; and a fluid circuit comprising, in turn, a first branch for interconnecting the electric pump and the piston pump, and a second branch for interconnecting the piston pump and the internal combustion engine.

As a general rule, the fluid circuit comprises, additionally, a metering solenoid valve positioned on the first branch for the selective control of the instantaneous flow rate of fuel supplied to the piston pump as a function of the values of a plurality of operating parameters of the internal combustion engine, and a third branch, which interconnects the first branch and the containing tank, is connected to the first branch upstream of the metering solenoid valve in a direction of advance of the fuel along the first branch, and enables at least some of the flow of fuel in excess of that which is supplied through the metering solenoid valve to be discharged into the containing tank.

The third branch is provided with an overflow valve, which is mounted in a first mounting aperture formed through a pump housing of the piston pump, and has an inlet for the inflow of the fuel into the overflow valve, at least one outlet for the outflow of the fuel from the overflow valve, and a slide valve which is movable between a position which closes the outlet and a position which opens the outlet.

The third branch is also at least partially formed by a connector which is mounted in a second mounting aperture formed through the pump housing of the piston pump transversely with respect to the aforesaid first mounting aperture, is in fluid communication with the outlet of the overflow valve, and projects from the pump housing for connection to a pipe for supplying the fuel to the containing tank.

Known pump units of the type described above have a number of drawbacks, mainly due to the fact that the provision of two mounting apertures, namely one for the overflow valve and one for the connector, requires the execution of relatively complicated, lengthy and costly machining operations on the aforesaid pump housing.

The object of the present invention is to provide a pump unit for supplying fuel, preferably diesel oil, from a containing tank to an internal combustion engine which is free of the drawbacks described above and which is simple and economical to produce.

According to the present invention, a pump unit is provided for supplying fuel, preferably diesel oil, from a containing tank to an internal combustion engine, as claimed in the appended claims. The present invention will now be described with reference to the attached drawings, which show a non-limiting example of its embodiment, in which:

Figure 1 is a fluid diagram of a preferred embodiment of the pump unit of the present invention;

Figure 2 is a schematic view, with parts in section and parts removed for clarity, of a detail of the pump unit of Figure 1; Figure 3 is a schematic view, with parts in section and parts removed for clarity, of a variant of the detail of Figure 2; and

Figure 4 is a schematic perspective view of the variant of Figure 3.

With reference to Figure 1, the number 1 indicates the whole of a pump unit for supplying a liquid fuel, preferably diesel oil, from a containing tank 2 to an internal combustion engine 3, in the present case a diesel engine comprising a fuel distribution manifold 4, commonly known as a "common rail", and a plurality of injectors 5 connected to the manifold 4 and adapted to spray the fuel into corresponding combustion chambers (not shown) of the engine 3.

The pump unit 1 comprises a high-pressure pump 6, in the present case a piston pump, adapted to supply the fuel to the engine 3, and a low-pressure or pre-feed pump, in the present case an electric pump, adapted to supply the fuel from the tank 2 to the pump 6.

The pump 6 comprises a pump housing 8 having a specified longitudinal axis 9, and at least one cylinder 10, which is formed in the pump housing 8, has a longitudinal axis 11 substantially perpendicular to the axis 9, and is engaged slidably by a piston 12.

The piston 12 is moved along the cylinder 10 by an actuator 13 of a known type fitted in the pump housing 8 and having a reciprocating rectilinear motion comprising an outward stroke for drawing the fuel into the cylinder 10 and a return stroke for compressing the fuel contained in the cylinder 10.

The pump unit 1 also comprises a fluid circuit 14 for supplying the fuel, comprising, in turn, a first branch 15, which interconnects the pumps 6 and 7, extends through the pump housing 8 to lubricate the actuator 13, and is connected to the cylinder 10 through an intake valve 16, and a second branch 17, which extends between the pump 6 and the manifold 4, and is connected to the cylinder 10 through a delivery valve 18. The branch 15 is provided with a metering solenoid valve 19, which is mounted upstream of the valve 16 in a direction 20 of advance of the fuel along the branches 15 and 17, is movable between a position which closes the branch 15 and a position which opens it, and is adapted to control selectively the instanta- neous flow rate of fuel supplied to the pump 6 as a function of the values of a plurality of operating parameters of the engine 3.

The circuit 14 also comprises a third branch 21, which connects the branch 15 upstream of the solenoid valve 19 in the direction 20 to the tank 2, and enables at least some of the flow of fuel in excess of that which is supplied through the solenoid valve 19 to be discharged into the tank 2, and a fourth branch 22, which extends between the manifold 4 and the branch 21, and enables the flow of fuel in excess of that required by the injectors 5 to be discharged into the tank 2. The circuit 14 also has a fifth branch 23 for discharging into the branch 21, and consequently into the tank 2, any fuel supplied through the pump housing 8 from the branch 15 and leaking through the support bearings (not shown) of the actuator 13, and a sixth branch 24, which is connected to the branch 15 downstream of the solenoid valve 19 in the direction 20, extends between the branch 15 and the branch 21, allows the absorption of the flow of fuel leaking through the solenoid valve 19 when the solenoid valve 19 is closed, and is provided with a calibrated aperture 25 designed so as to limit the quantity of fuel absorbed by the branch 24 to a value below a specified threshold when the solenoid valve 19 is open. As shown in Figures 1 and 2, the branch 21 is provided with an overflow valve 26 mounted in a mounting aperture 27 which is formed through the pump housing 8, has a specified longitudinal axis 28, and comprises a constricted portion 27a and a wider portion 27b, interconnected by an annular shoulder 29 which is substantially transverse with respect to the axis 28.

The valve 26 comprises a substantially cylindrical valve housing 30, which extends coaxially with the axis 28, is mounted in the aperture 27 by means of an interposed ring seal 31, has an axial aperture 32 for the entry of fuel into the valve housing 30, and is provided with at least two radial apertures for the outflow of the fuel from the valve housing 30.

The valve 26 also comprises a slide valve 34, which is mounted in the valve housing 30 coaxially with the axis 28, is moved to, and normally kept in, a position which closes the apertures 33 (Fig. 2) by a spring 35 interposed between the valve housing 30 and the slide valve 34, and is moved by the fuel against the action of the spring 35 from the position which closes the apertures 33 to a position (not shown) which opens the apertures.

The fuel supplied through the apertures 33 as a result of the movement of the slide valve 34 to its open position is collected in a portion 36 of the aperture 27 which can also receive the fuel from the branch 23.

The branch 31 also comprises a tubular connector 37 made in one piece with the valve housing 30 so as to form a single sleeve 38, this sleeve being locked by interference in the portion 27b coaxially with the axis 28.

The connector 37 is connected to a pipe (not shown) forming part of the branch 21, and communicates with the portion 36 through at least two connecting apertures 39, which are formed through the sleeve 38 and are inclined with respect to the axis 28.

The variant shown in Figures 3 and 4 differs from that shown in Figure 2 solely in that, in this variant, the valve housing 30 and the connector 37 are two separate pieces which are distinct from each other, and in that the valve housing 30 has at least two radial slits 40, which are distributed uniformly around the axis 28, and are formed through the valve housing 30 on corresponding flat faces 41 formed on an outer surface of the valve housing 30.

The valve 26 is coupled slidably to the aperture 27, and is locked axially against the shoulder 29 by the connector 37, which in turn is locked by interference in the portion 27b, and communicates with the portion 36 through the slits 40 and the corresponding faces 41. In a variant which is not illustrated, the valve housing 30 is also locked by interference in the aperture 27. The mounting of the overflow valve 26 and of the connector 37 in a single mounting aperture 27 enables the structure of the pump housing 8 to be simplified and enables the machining costs and times of the pump housing 8 to be reduced.