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 piston pump for feeding fuel to an internal combustion engine; a gear pump for feeding the fuel from a storage tank to the piston pump; and a hydraulic circuit for connecting together the storage tank, the gear pump, the piston pump and the internal combustion engine.

The gear pump comprises a pump body, which has a cup-like shape, is bounded by a substantially flat bottom wall and by a shaped side wall and is closed by a lid mounted in contact with the pump body parallel to the said bottom wall.

The pump body and the lid define a containing chamber which has inlet for supplying the fuel into the gear pump and an outlet for discharging the fuel from the gear pump and houses inside it two gears which are engaged together so as to rotate about respective axes of rotation substantially parallel to each other and perpendicular to the bottom wall and to the lid.

The gears are engaged such that one is angularly fixed to a transmission shaft extending through the bottom wall and the other one is rotatable about a support pin projecting from said bottom wall.

Each gear is subjected to a thrust obtained as the resultant of a hydraulic force generated by the pressure difference existing between the outlet and the inlet of the containing chamber and a mechanical force generated by the interaction between the two gears.

The known pumping units of the type described above, although tried-and-tested, have a number of drawbacks mainly due to the fact that the thrust exerted on each gear is transverse to the associated axis of rotation and generates a bending moment on the gear itself.

Owing to the play existing between the pump body, the lid and the gears, the bending moment acting on each gear causes the displacement of the gear into contact with the bottom wall and/or side wall and/or the lid of the containing chamber, the frictional contact of the gear on the bottom wall and/or on the side wall and/or on the lid of the containing chamber and the asymmetrical wear of the pump body and the lid and adversely affects the correct operation of the pumping unit.

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 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 attached 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:

Figures 1 is a hydraulic diagram of a preferred embodiment of the pumping unit according to the present invention;

Figure 2 is a schematic front-end view, with parts removed for greater clarity, of a detail of the pumping unit according to Figure 1; and Figure 3 is a schematic cross-section, with parts removed for greater clarity, of the detail according to Figure 2.

With reference to Figure 1, 1 denotes in its entirety a pumping unit for feeding 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 referred to 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 said engine 3.

The pumping unit 1 comprises a high-pressure pump 6 for feeding the fuel to the engine 3; and a low-pressure or pre-feed pump 7 for feeding the fuel from the tank 2 to the pump 6.

The pump 6 is a piston pump comprising 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.

According to a variant not shown, the number of cylinders 9 is different from two, and in particular equal to one, and the axes 10 are not 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 further comprises, for each piston 11, a respective spring (not shown) 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 displace simultaneously one piston 11 with its intake stroke and the other piston 11 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 advancing movement 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 said electrovalve 20 is closed.

The circuit 15 also has a sixth line 26, which extends between the line 17 and the pump body 8, 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 chamber 14 of the fuel flow used to lubricate the cam transmission shaft 13 and the flow of fuel in excess of that fed across the electrovalve 20. The circuit 15 comprises finally a seventh line 28 for feeding into the line 24 and therefore into the line 16 the fuel seeping through the pump body 8.

According to that shown in Figures 2 and 3, the pump 7 is a gear pump comprising a pump body 29 which is fixed to the pump body 8 and has a cup shaped form.

The pump body 29 is bounded by a substantially flat bottom wall 30 perpendicular to an axis of rotation of the shaft 13 and is also bounded by a shaped side wall 32.

The pump body 29 is closed by a lid 33 which is mounted in contact with the pump body 29 parallel to the wall 30 and defines, together with the pump body 29 itself, a containing chamber 34 having an inlet 35 for supplying the fuel into the pump 7 and an outlet 36 for discharging the fuel from said pump 7.

The chamber 34 houses internally a pair of cylindrical gears 37, 38 which are engaged together.

The gear 37 is angularly fixed to a free end of the shaft 13 projecting inside the chamber 34 and is displaced by the shaft 13 about the axis 31.

The gear 38 is fitted rotatably onto a support pin 30 which has a longitudinal axis 40 parallel to the axis 31 and projects axially from the wall 30.

Each gear 37, 38 is subject to a thrust FI obtained as the resultant of a hydraulic force generated by the pressure difference existing between the outlet 36 and the inlet 35 of the chamber 34 and a mechanical force generated by the interaction between the two gears 37,38.

The thrust FI acting on each gear 37, 38 is transverse to the associated axis of rotation 31,40, in particular radial, lies in a plane P parallel to said associated axis of rotation 31, 40 and is arranged at an angle other than 0° with respect to the thrust FI acting on the other gear 37, 38. Owing to the tolerances and the existing play, each gear 37, 38 is subject to a bending moment Ml generated by the associated thrust FI.

The circuit 15 also comprises an eighth line 41 which extends between one of the cylinders 9 and the chamber 34 and has a smaller cross-section, in the case in question a calibrated hole 42, designed to control feeding of the fuel along said line 41.

According to a variant, not shown, the line 41 extends between the line 18 and the chamber 34.

In the case in question, therefore, the line 41 receives at its input fuel at the delivery pressure of high-pressure pump 6.

The line 41 communicates with the chamber 34 by means of two feeder holes 34, each of which is formed through the lid 33 and is eccentric with respect to the associated axis 31, 40.

Each hole 43 faces a larger face 44 of the associated gear 37, 38 substantially perpendicular to the associated axis 31, 40 and is arranged, in the case in question, in the corresponding plane P.

The fuel fed into the chamber 34 through each hole 43 exerts on the face 44 of the associated gear 37, 38 a hydraulic thrust F2 oriented - preferably but not necessarily - parallel to the associated axis 31, 40.

Each thrust F2 generates on the associated gear 37, 38 a bending moment M2 opposite to the corresponding bending moment Ml.

It should be pointed out that the pressure of the fuel fed into the chamber 34 through the holes 43 is greater than the delivery pressure of the pump 7 at the outlet 36. The pump 7 has some advantages mainly derived from the fact that the thrust F2 and the bending moment M2 ensure a relatively smaller wear and correct lubrication of the pump body 29, the lid 33 and the gears 37, 38.