Title

PUMPING UNIT FOR FEEDING FUEL, PREFERABLY DIESEL FUEL, TO AN INTERNAL COMBUSTION ENGINE

The present invention relates to a pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine.

In particular the present invention relates to a pumping unit of the type comprising a high-pressure pump, for example a piston pump, designed to feed the fuel to an internal combustion engine; a pre-feed pump, for example a gear pump, designed to feed the fuel from a storage tank to the piston pump; and a hydraulic circuit for connecting together the storage tank and the internal combustion engine.

The piston pump comprises a pump body; at least two cylinders formed in the pump body and slidably engaged by respective pistons; and an actuating device for displacing the pistons along the associated cylinders with a reciprocating rectilinear movement comprising an intake stroke for drawing the fuel into the cylinders and a delivery stroke for supplying the fuel to the internal combustion engine.

The two cylinders have respective longitudinal axes which are parallel to each other and are each associated with a respective intake valve for drawing the fuel into the cylinder and with a respective delivery valve for supplying the fuel to the internal combustion engine.

The actuating device is configured so as to displace simultaneously a piston with its intake stroke and the other piston with its delivery stroke. The hydraulic circuit comprises a first line for connecting together the storage tank and the gear pump; a second line for connecting together the gear pump and the piston pump; and a third line for connecting together the piston pump and the internal combustion engine.

The second line comprises a feed header and, for each cylinder, a respective intake duct for connecting the feed header to the said cylinder.

Generally, the hydraulic circuit further comprises a metering electrovalve arranged along the second line for selectively controlling the instantaneous flow of fuel fed to the piston pump depending on the values of a plurality of operating parameters of the internal combustion engine.

The known pumping units of the type described above have a number of drawbacks mainly resulting from the fact that the pressure waves generated in each intake duct by closing of the associated intake valve advance, via the feed header, along the other intake duct and may compromise the correct opening of the associated intake valve, and therefore the correct filling of the associated cylinder.

The object of the present invention is to provide a pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine, which does not have the aforementioned drawbacks and which is simple and inexpensive to produce.

According to the present invention a pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine is provided, as claimed in the accompanying claims.

The present invention will now be described with reference to the accompanying drawings which illustrate a non-limiting example of embodiment thereof, in which:

Figure 1 is a hydraulic diagram of a preferred embodiment of the pumping unit according to the present invention; Figure 2 is a schematic perspective view, with parts cross-sectioned, of a detail of the pumping unit of Figure 1; and

Figure 3 is a perspective view of a detail of Figure 2.

With reference to Figure 1, 1 denotes in its entirety a pumping unit for feeding a fuel, preferably diesel fuel, from a storage tank 2 to an internal combustion engine 3, in the case in question a diesel combustion engine.

The engine 3 comprises a header 4 for distribution of the fuel, commonly known by the term "common rail", and a plurality of injectors 5 connected to the header 4 and designed to atomize the fuel inside associated combustion chambers (not shown) of the said engine 3.

The pumping unit 1 comprises a high-pressure pump 6, namely a piston pump, for feeding the fuel to the engine 3; and a low-pressure or pre-feed pump 7, namely a gear pump, which is for example electrically operated, for feeding the fuel from the tank 2 to the pump 6.

The pump 6 comprises a pump body 8 and, in this case, two cylinders 9, which are formed in the pump body 8 and have respective longitudinal axes 10 substantially parallel to each other.

The cylinders 9 are slidably engaged by respective pistons 11 movable, under the thrust of an actuating device 12, with an alternating rectilinear movement comprising an intake stroke for drawing the fuel inside the associated cylinders 9 and a delivery stroke for supplying the fuel to the engine 3.

The device 12 comprises a cam transmission shaft 13 which is housed inside a first containing chamber 14 formed in the pump body 8 and is designed to displace the pistons 11 with their delivery stroke. The device 12 also comprises, for each piston 11, a respective spring (not shown) which is housed inside a second containing chamber (not shown) formed in the pump body 8 and is designed to displace said piston 11 with its intake stroke.

In connection with the above description it should be pointed out that the shaft 13 is configured so as to allow the pistons 11 to be displaced simultaneously, one with its intake stroke and the other with its delivery stroke.

The pumping unit 1 also comprises a hydraulic circuit 15 comprising, in turn, a first line 16 for connecting together the tank 2 and the pump 7; a second line 17 for connecting together the pump 7 and the pump 6; and a third line 18 for connecting together the pump 6 and the header 4.

The line 17 is provided with a filtering device 19 for filtering the fuel fed to the cylinders 9 and also has a metering electrovalve 20, mounted downstream of the device 19 in a direction 21 of flow of the fuel along the line 17, for selectively controlling the instantaneous flowrate of the fuel fed to the pump 6 depending on the values of a plurality of operating parameters of the engine 3.

The line 17 and the line 18 are connected to each cylinder 9 by means of an intake valve 22 and a delivery valve 23, respectively.

The circuit 15 also comprises a fourth line 24, which extends between the header 4 and the line 16 and allows the fuel flow which exceeds that needed for the injectors 5 to be discharged into the line 16; and a fifth line 25 which extends between the line 17 and the line 16 and is connected to the line 17 downstream of the electrovalve 20 in the direction 21 for feeding to the inlet of the pump 7 the fuel seeping through the electrovalve 20 when the said electrovalve 20 is closed.

The circuit 15 also has a sixth line 26 which extends between the line 17 and the line 24, is connected to the line 17 upstream of the electrovalve 20 in the direction 21 and is provided with a valve device 27. The device 27 is configured to control the supply into the pump body 8 and into the containing chamber 14 of the fuel flow used to lubricate the cam transmission shaft 13 and the fuel flow in excess of that fed through the electrovalve 20.

The circuit 15 comprises, finally, a seventh line 28 for feeding into the line 26 and therefore into the tank 2 the fuel seeping through the pump body 8.

In accordance with that shown in Figures 2 and 3, the line 17 comprises a feed header 29 and, for each cylinder 9, a respective intake duct 30 for connecting the header 29 to said cylinder 9.

Internally, the header 29 houses a flow separator 31 designed to divide the fuel supplied by the pump 7 into two fuel flows, each of which is advanced along an associated duct 30 to the associated intake valve 22.

The separator 31 is mounted downstream of the electrovalve 20 in the direction 21, and comprises a separator element 32, which has the form of a flat plate and is designed to divide the header 29 into two separate feed channels 33 each connected to an associated duct 30.

The separator 31 also comprises a coupling element 34, which has the form of a cylindrical hub, is integral with the element 32, and is slidably engaged in the header 29.

Since the ducts 30 are arranged in succession along the header 29, the element 34 is mounted between the two ducts 30, is configured in such a way as to axially close one of the channels 33 and divert the fuel into the associated duct 30, and also has an opening 35 designed to allow the fuel fed along the other channel 33 to advance through the separator 31 and into the associated duct 30.

Since the pressure waves generated by the closing of each intake valve 22 advance along the associated intake duct 30 and the associated feed channel 33 without reaching the intake duct 30 of the other intake valve 22, the pumping unit 1 has a number of advantages mainly resulting from the fact that the flow separator 31 allows each intake valve 22 to operate independently of the other intake valve 22, and therefore ensures correct filling of the cylinders 9.