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, in this case a piston pump, for feeding the fuel to the internal combustion engine; and a pre-feed pump, for example a gear pump, for feeding the fuel from a storage tank to the high-pressure pump.

The pumping unit further comprises a hydraulic circuit comprising, in turn, a first line for connecting together the storage tank and the pre-feed pump, a second line for connecting together the pre-feed pump and the high-pressure pump, and a third line for connecting together the high-pressure pump and the internal combustion engine.

The hydraulic circuit further comprises a metering electrovalve mounted along the second line for selectively controlling the instantaneous flow of fuel fed to the high-pressure pump depending on the values of a plurality of operating parameters of the internal combustion engine.

The hydraulic circuit further comprises a fourth line which is connected to the second line upstream of the metering electrovalve in a direction of flow of the fuel along said second line, extends through an overflow valve and is also connected to the storage tank so as to discharge therein at least some of the fuel flow in excess of that fed through the metering electrovalve. The high-pressure pump is a piston pump comprising a pump body; at least one cylinder formed in the pump body; a piston slidably engaged in the cylinder; and an actuating device for displacing the cylinder with an intake stroke for drawing the fuel into the cylinder and with a compression stroke for compressing the fuel contained inside said cylinder.

The actuating device comprises a transmission shaft mounted through the pump body so as to rotate about an axis of rotation transverse to a longitudinal axis of the cylinder and displace the piston with its compression stroke; and a spring arranged between the pump body and the piston so as to displace said piston with its intake stroke.

The transmission shaft projects outside the pump body, is rotatably coupled with the pump body via a pair of support bearings and is coupled in fluid-tight manner with said pump body via an annular seal.

The annular seal defines, together with the pump body and the transmission shaft, a chamber for collecting the fuel seeping between one of the support bearings and said transmission shaft.

The hydraulic circuit further comprises a fifth line for connecting together the collection chamber and the fourth line and for discharging into the storage tank the fuel contained in said collection chamber.

The pumping units of the known type described above have a number of drawbacks mainly due to the fact that the outflow of the fuel from the collection chamber into the storage tank is hindered by the relative small pressure difference between the collection chamber and the storage tank and the fact that consequently the annular seal is subject to a relatively high pressure which may cause fuel leakages through said annular seal. 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 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:

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

Figures 2 and 3 are two schematic cross-sectional views, with parts removed for greater clarity, of the pumping unit according to Figure 1.

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 this case 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 able 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, in this case a gear pump or electric pump, for feeding the fuel from the tank 2 to the pump 6.

In accordance with that shown in Figures 1, 2 and 3, the high-pressure pump 6 is a piston pump provided with a pump body 8 comprising a containing housing 9 which has a central hole 10 with a longitudinal axis 11 and also has at least one lateral hole 12 (normally a plurality of holes 12 uniformly distributed around the axis 11), which has a longitudinal axis transverse to the axis 11 and extends radially towards the outside of the housing 9 from said hole 10.

Each hole 12 is closed by a head-piece 14 which is arranged in contact with the housing 9 and has an appendage 15 projecting inside the hole 12 coaxially with the axis 13.

The head-piece 14 has a central hole 16 which is formed through the head-piece 14 coaxially with the axis 13 and comprises a wide portion 17 and a narrow portion 18 which are aligned with each other along said axis 13.

The portion 18 faces the hole 10 and defines a cylinder 19 of the pump 6. The cylinder 19 is slidably engaged by a piston 20 movable, under the thrust of an actuating device 21, with an alternating rectilinear movement comprising an intake stroke for drawing the fuel into the cylinder 19 and a compression stroke for compressing the fuel contained inside said cylinder 19.

The device 21 comprises a tubular sleeve 22 which is slidably engaged inside the hole 12 coaxially with the axis 13, extends around the cylinder 19 and has an internal annular flange 23.

The flange 23 projects radially from an inner surface of the sleeve 22 and divides said sleeve 22 into two cylindrical portions 24, 25, the portion 24 of which faces the hole 10.

The device 21 also has a tappet system 26 comprising a coupling block 27 with a substantially cylindrical shape, which is locked by means of interference inside the portion 24, is arranged in contact with the flange 23 and supports a tappet system roller 28.

The roller 28 projects from the block 27 towards the hole 10 and is rotatably coupled with the block 27 so as to rotate, relative to said block 27, about its longitudinal axis 29 substantially perpendicular to the axis 13. The flange 23 supports an annular disc 30 which extends around the piston 20, is inserted inside the portion 25 of the sleeve 22 coaxially with the axis 13 and has an outer perimeter edge axially facing the flange 23 and an inner perimeter edge axially facing a head of said piston 20.

The device 21 further comprises a compression spring 31 which is mounted between the appendage 15 and the sleeve 22 coaxially with the axis 13 and is arranged between the head-piece 14 and the disc 30 so as to displace, and normally keep, the disc 30 in contact with the flange 23 and the roller 28 in contact with a cam 32 formed on an outer surface of an intermediate portion of a transmission shaft 33.

The shaft 33 extends through the hole 10 and is rotatably coupled with the housing 9 via two support bearings 34, 35 so as to rotate, relative to said housing 9, about the axis 11.

The shaft 33 also has a free end which extends outside the pump body 8 and is coupled in a fluid-tight manner with the pump body 8 via an annular seal 36 mounted between the housing 9 and the shaft 33 coaxially with the axis 11.

The seal 36 defines, together with the pump body 8 and the shaft 33, a chamber 37 for collecting the fuel seeping between the shaft 33 and the bearing 34.

The feeding of the fuel inside each cylinder 19 is selectively controlled by an associated intake valve 38 of the known type and feeding of the fuel from each cylinder 19 to the internal combustion engine 3 is selectively controlled by an associated delivery valve 39 of the known type.

The pumping unit 1 further comprises a hydraulic circuit 40 comprising, in turn, a first line 41 for connecting together the tank 2 and the pump 7; a second line 42, which connects together the pumps 6 and 7, extends through the pump body 8 and the hole 10 in order to lubricate the shaft 33 and is connected to the cylinder 19 by means of the intake valve 38; and a third line 43 which extends between the pump 6 and the header 4 and is connected to the cylinder 19 by means of the delivery valve 39.

The line 42 is provided with a metering electrovalve 44 which is movable between a position for closing and a position for opening the line 42 and is designed to control selectively the instantaneous flowrate of fuel fed to the pump 6 depending on the values of a plurality of operating parameters of the engine 3.

The circuit 40 further comprises a fourth line 45 which is connected to the line 42 upstream of the electrovalve 44 in a direction 46 of flow of the fuel along the lines 41, 42 and 43, is also connected to the tank 2 and extends through an overflow valve 47 and allows discharging into the tank 2 of at least some of the fuel flow in excess of that fed through said electrovalve 44.

The circuit 40 also has a fifth line 48 which extends between the header 4 and the line 45 and allows the fuel flow in excess of that needed for the injectors 5 to be discharged into the tank 2.

The circuit 40 further comprises a sixth line 49 for discharging into the line 45, and therefore into the tank 2, the fuel fed through the pump body 8 and the hole 10 from the line 42 and seeping between the pump body 8 and the bearing 35.

The collection chamber 37 and the line 41 are connected together by means of a seventh line 50 of the circuit 40 designed to discharge to the inlet of the pump 7 the fuel seeping between the shaft 33 and the bearing 34 inside said chamber 37.

The circuit 40, finally, is provided with an eighth line 51, which is connected to the line 42 downstream of the electrovalve 44 in the direction 46, is also connected to the line 50 and allows the fuel seeping through the electrovalve 44 when said electrovalve 44 is closed to be discharged into the line 50 and therefore to the inlet of the pump 7.

Since the pressure in the line 41 is less than atmospheric pressure owing to the suction action of the pump 7 which draws from the tank 2 and the pressure inside the chamber 37 is greater than atmospheric pressure, the pumping unit 1 has a number of advantages mainly due to the fact that the pressure difference between the chamber 37 and the line 41 is relatively high and facilitates the outflow of the fuel from the chamber 37 into the line 41 along the line 50.

Consequently the seal 36 is subject to relatively small stresses, and the fuel losses from the chamber 37 across said seal 36 are also relatively small.

Similarly, the pressure difference between the line 42 and the line 41 is relatively high and facilitates the outflow of the fuel from the line 42 into the line 41 along the line 51.