Title: PUMP UNIT FOR SUPPLYING FU EL, PREFERABLY DI ESEL OIL, TO AN

INTERNAL COMBUSTION ENGINE

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

In particular, the present invention relates to a pump unit of the type comprising a high-pressure pump for supplying the fuel to the internal combustion engine and a pre-supply pump for supplying the fuel to the high-pressure pump.

Generally, the high-pressure pump comprises a pump body having a central bore and at least two lateral bores, which have respective longitudinal axes parallel to one another and perpendicular to a longitudinal axis of the central bore, and face toward this central bore.

Each lateral bore houses within it a tubular head comprising a constricted portion forming a cylinder of the high-pressure pump and a widened portion connected to the constricted portion at an annular shoulder.

The fuel is supplied into the cylinder through an intake valve, which comprises a valve body mounted in the widened portion in contact with the annular shoulder, and has a shutter member mounted through the valve body so as to move between an open and a closed position of the intake valve.

The head is closed axially by a plug screwed into the widened portion to lock the valve body axially against the annular shoulder. Each head also has a conduit for supplying fuel to the widened portion of the head, and then to the intake valve, and houses within it a delivery valve for selectively controlling the supply of fuel to the internal combustion engine.

The cylinders are slidingly engaged by respective pistons which can move with a reciprocating rectilinear motion along the corresponding cylinders under the force imparted by a drive device, comprising a transmission shaft mounted rotatably through the aforesaid central bore of the pump body and, for each piston, a respective spring interposed between the head and the piston.

Each piston is moved by the corresponding spring in a stroke for the intake of fuel into the corresponding cylinder, and by the transmission shaft in a stroke for the delivery of the fuel from the corresponding cylinder to the internal combustion engine.

Since each head includes the structure of the corresponding supply conduit and the screw thread of the corresponding widened portion, known pump units of the type described above have a number of drawbacks, mainly due to the fact that the production cycle for the corresponding heads is relatively complex and costly.

Furthermore, because of the presence of a closing plug for each head, the pump units have a relatively large number of components and a relatively long assembly time, while, owing to the presence of the conduits for supplying fuel to the cylinders, the overall dimensions and weights of the heads are relatively high.

The object of the present invention is to provide a pump unit for supplying fuel, preferably diesel oil, 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, to an internal combustion engine, as claimed in the appended claims. The present invention will now be described with reference to the attached drawing which shows, in cross section and with parts removed for clarity, a non- limiting exemplary embodiment of the invention.

With reference to the attached figure, the number 1 indicates the whole of a pump unit for supplying fuel, preferably diesel oil, to an internal combustion engine (not shown).

The pump unit 1 comprises a high-pressure pump, in the present case a piston pump 2, for supplying the fuel to the aforesaid internal combustion engine (not shown); and a pre-supply pump, in the present case a gear pump 3, for supplying the fuel to the pump 2.

The pump 2 comprises, in the present case, a pump body 4, which is provided with a central bore 5 having a longitudinal axis 6, and is also provided with a plurality of lateral bores 7 (two lateral bores 7 in the present case), which have respective longitudinal axes 8 parallel to one another and perpendicular to the axis 6, and which face toward the bore 5.

Each bore 7 houses within it a tubular head 9, which is fixed to the pump body 4, projects inside the bore 7, and extends around the corresponding axis 8.

Each head 9 comprises a constricted portion forming a cylinder 10 of the pump 2, and a widened portion 11 limited axially by a free end surface 12 perpendicular to the corresponding axis 8 and coplanar with the surface 12 of the other head 9.

Each cylinder 10 is slidingly engaged by a piston 13, which projects outside the cylinder 10 and forms, together with the cylinder 10, a variable-volume chamber 14.

The chamber 14 communicates with the portion 11 via an interposed intake valve 15 comprising a valve body 16, which is incorporated in the head 9, is made in one piece with the head 9, and is formed by an annular flange which projects radially toward the inside of a lateral surface of the head 9 and extends coaxially with the axis 8.

The valve 15 also comprises a shutter member 17 which extends through the valve body 16 coaxially with the axis 8, is movable between an open and a closed position of the valve 15, and is moved to, and normally kept in, its closed position by a spring 18 interposed between the head 9 and the member 17.

The chamber 14 is also connected to a conduit (not shown) for delivering the fuel to the internal combustion engine (not shown) via a delivery valve 19 of a known type formed in the head 9.

The pistons 13 are moved by a drive device 20 along the corresponding cylinders 10 with a reciprocating rectilinear motion, comprising a stroke for the intake of the fuel into the corresponding chambers 14 and a stroke for delivering the fuel to the internal combustion engine (not shown).

The device 20 comprises, for each piston 13, a respective tubular sleeve 21, which is slidingly engaged inside the corresponding bore 7, extends around the corresponding cylinder 10, and has an annular flange 22, which projects radially into the sleeve 21 to divide it into two cylindrical portions 23 and 24, of which the portion 24 faces toward the bore 5.

The device 20 also has, for each sleeve 21, a respective cam follower 25 comprising a coupling block 26 of substantially cylindrical shape, which is fitted inside the corresponding portion 24, is positioned in contact with the

corresponding flange 22, and is locked by interference inside the corresponding portion 24.

The cam follower 25 also comprises a cam follower roller 27, which projects from the block 26 toward the bore 5, and is coupled rotatably to the block 26 so as to rotate, relative to the block 26, about its own longitudinal axis 28, which is substantially perpendicular to the corresponding axis 8. The portion 23 houses within it an annular plate 29, which extends around the piston 13 coaxially with the axis 8, and has an inner perimetric edge facing axially toward the head of the piston 13 and an outer perimetric edge facing the flange 22.

The device 20 also comprises, for each piston 13, a respective cylindrical spring 30, which is mounted inside the corresponding bore 7, and extends between the corresponding head 9 and the corresponding sleeve 21 coaxially with the corresponding axis 8.

The springs 30 are interposed between the corresponding heads 9 and the corresponding plates 29, in order to position, and normally keep, the plates 29 in contact with the corresponding flanges 22 and the corresponding pistons 13; to position, and normally keep, the pistons 13 in contact with the corresponding cam followers 25; and to position, and normally keep, the corresponding rollers 27 in contact with respective cams 31 formed on an outer surface of a transmission shaft 32 mounted through the bore 5 so as to rotate about the axis 6 relative to the pump body 4.

The pump unit 1 also comprises a single cover 33 for closing the widened portions 11 of all the heads 9, and a hydraulic circuit 34 for supplying the fuel to the portions 11 and then to the chambers 14.

The cover 33 comprises a closure plate 35 positioned in contact with the surfaces 12 and a centering shank 36 which projects from the plate 35 perpendicularly to the surfaces 12, and is engaged between the two heads 9.

The circuit 34 is formed entirely outside the heads 9, and comprises a distribution manifold 37 comprising, in turn, in the present case, a first portion 38 formed through the pump body 4 and a second portion 39 formed through the cover 33.

The circuit 34 also comprises, for each cylinder 10, a respective supply conduit 40 formed through the cover 33 to connect the manifold 37 and the

corresponding portion 11 to one another. Since the supply conduits 40 are formed through the cover 33 and not through the heads 9, the heads 9 have relatively small dimensions, overall dimensions and weights.

Since the valve bodies 16 of the intake valves 15 are incorporated into the heads 9, the forces due to the compression of the fuel contained in the chambers 14 act on the heads 9, and not on the cover 33, which can therefore be made of a relatively cheap material such as aluminum or plastic material.

Moreover, the presence of a single cover 33 makes it possible to reduce the number of components and the assembly time of the pump unit 1.

According to some variants which are not shown: the two heads 9 are dispensed with, and are replaced with a single head including both cylinders 10; the distribution manifold 37 is dispensed with, and is replaced with a distribution manifold formed entirely through the cover 33; and the cover 33 houses within it at least one flow rate regulation valve for regulating the flow rate of fuel supplied to the cylinders 10.