Title

PUMPING UNIT FOR FEEDING A FLUID, IN PARTICULAR FUEL, PREFERABLY DIESEL FUEL, TO A USER APPLIANCE, IN PARTICULAR AN

INTERNAL COMBUSTION ENGINE

The present invention relates to a pumping unit for feeding a fluid, in particular fuel, preferably diesel fuel, to a user appliance, in particular an internal combustion engine.

The present invention has a particularly advantageous application in the feeding of fuel, preferably diesel fuel, to an internal combustion engine, to which the description below specifically refers without thereby losing its general character.

The pumping unit comprises a high-pressure pump for feeding fuel to an internal combustion engine; and a low pressure or pre-feed pump for feeding fuel from a storage tank to the said high-pressure pump.

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 inside the cylinder; and an actuating device for displacing the cylinder with an alternating rectilinear movement comprising an intake stroke for drawing the fuel into the cylinder and a delivery stroke for supplying the fuel to the internal combustion engine. The high-pressure pump further comprises an intake valve for selectively controlling feeding of the fuel into the cylinder; and a delivery valve for selectively controlling feeding of the fuel to the internal combustion engine.

The intake valve comprises a valve body with a cylindrical shape, mounted and fixed inside the pump body, and a closing member engaged slidably through the valve body so as to be displaced between an open position and a closed position of the cylinder.

When the closing member is arranged in its closed position, the closing member and the valve body are engaged with each other in a fluid-tight manner in a sealing zone defined by respective engaging surfaces. During use, the delivery stroke of each piston causes closing of the associated intake valve. During closure of the intake valve, a part of fuel compressed by the piston exits the cylinder between the valve body and the closing member.

The known pumping units of the type described above have a number of drawbacks mainly resulting from the fact that the fuel exiting the cylinder during the delivery stroke of the piston is subject, in the aforementioned sealing zone, to cavitation effects, namely the formation of vapour bubbles which, following the subsequent renewed filling of the cylinder with fuel supplied by the pre-feed pump, implode, generating noise, causing wear and erosion of the said engaging surfaces and therefore adversely affecting the fluid-tight connection between the closing member and the valve body.

The object of the present invention is to provide a pumping unit for feeding a fluid, in particular fuel, preferably diesel fuel, to a user appliance, in particular 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 a fluid, in particular fuel, preferably diesel fuel, to a user appliance, in particular 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 first schematic cross-sectional view, with parts removed for greater clarity, of a preferred embodiment of the pumping unit according to the present invention;

Figure 2 is a schematic cross-sectional view, with parts removed for greater clarity, of the pumping unit according to Figure 1;

Figure 3 is a schematic cross-sectional view, on a larger scale, of a detail of the pumping unit shown in Figures 1 and 2; Figure 4 is a schematic cross-sectional view, with parts removed for greater clarity, of a variant of the pumping unit according to Figures 1 and 2; and

Figure 5 is a schematic cross-sectional view, on a larger scale, of a detail of the pumping unit shown in Figure 4.

With reference to Figures 1 and 2, 1 denotes in its entirety, a pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine (not shown). The pumping unit 1 comprises a high-pressure pump 2 for feeding the fuel to the said internal combustion engine (not shown); and a low-pressure or pre-feed pump 3 for feeding the fuel from a known storage tank (not shown) to said pump

2. The high-pressure pump 2 is a piston pump and has a pump body 4 comprising a support housing 5 which is provided with a central hole 6 having a longitudinal axis 7 and is also provided with at least one side hole 8 (normally a plurality of holes 8 uniformly distributed around the axis 7) having a longitudinal axis 9 transverse to the axis 7 and extending radially towards the outside of the casing 5 from the said hole 6.

Each hole 8 is closed by a head-piece 10 which is arranged in contact with the housing 5 and has a lug 11 projecting inside the hole 8 coaxially with the axis 9. The head-piece 10 has a central hole 12 which is formed through the head-piece 10 coaxially with the axis 9 and comprises a wider portion 17a and a narrower portion 13b which are aligned with each other along said axis 9. The portion 13b faces the hole 6 and defines a cylinder 14 of the piston pump 2.

The cylinder 14 is slidably engaged by a piston 15 movable, as a result of the thrust of an actuating device 16, with an alternating rectilinear movement comprising an intake stroke for drawing the fuel into the cylinder 14 and a delivery stroke for supplying the fuel to the said internal combustion engine (not shown).

The device 16 comprises a tubular sleeve 17 which is slidably engaged inside the hole 8 coaxially with the axis 9, extends around the cylinder 14 and has an inner annular flange 18 which projects radially from an inner surface of the sleeve 17 and divides said sleeve 17 into two cylindrical portions 19, 20, the portion 19 of which faces the hole 6.

The device 16 also has a tappet system 21 comprising a coupling block 27 with a substantially cylindrical shape, which is locked by means of interference inside the portion 19, is arranged in contact with the flange 18 and supports a tappet system roller 23. The roller 23 projects from the block 22 towards the hole 6 and is rotatably coupled with the block 23 so as to rotate, relative to said block 22, about its longitudinal axis 24 substantially perpendicular to the axis 9.

The flange 18 supports an annular disk 25 which extends around the piston 15, is inserted inside the portion 20 of the sleeve 17 coaxially with the axis 9 and has an outer perimetral edge axially facing the flange 18 and an inner perimetral edge axially facing a head of said piston 15.

The device 16 also comprises a compression spring 26 which is mounted between the lug 11 and the sleeve 17 coaxially with the axis 9 and is arranged between the head-piece 10 and the disk 25 so as to displace, and normally keep, the disk 25 in contact with the flange 18 and the roller 23 in contact with a cam 27 formed on an outer surface of an intermediate portion of a transmission shaft mounted through the hole 6 so as to rotate, relative to the housing 5, about the axis 7.

The head-piece 10 houses internally an intake valve 29 for drawing the fuel into the cylinder 14 and a delivery valve 30 for supplying the fuel to the internal combustion engine (not shown).

The valve 29 is mounted inside the wider portion 13a of the hole 12 and comprises a valve body 31 with a cylindrical shape which extends around the axis 9 and is axially locked against an annular shoulder 32 defined between the portions 13a and 13b by a closing lid 33 screwed into the said portion 13a. The valve 29 also comprises a closing member 34 mounted though the valve body 31 so as to be displaced between a closed position, in which the closing member 34 engages in a fluid-tight manner with the valve body 31 in a sealing zone 35 so as to close the cylinder 14, and an open position.

In connection with the above description it should be pointed out that the sealing zone 35 may have the form of a circumferential line or a frustoconical surface.

The closing member 34 is displaced, and normally kept, in its closed position by a spring 36 arranged between the valve body 31 and an annular disc 37 mounted on the closing member 34 transversely with respect to the axis 9.

In accordance with that shown in Figure 3, the valve body 31 has a plurality of feeder holes 38 which are distributed around the axis 9 and have, in the case in question, respective longitudinal axes 39 which are substantially radial and transverse to the axis 9.

According to a variant (not shown), the axes 39 of the holes 38 are inclined with respect to the axis 9 and directed towards the cylinder 14.

The valve body 31 defines, together with the closing member 34, an intake chamber 49 configured so as to have a wider portion 41 and a narrower portion 42 arranged in succession and in this order from the outlet of the holes 38 to the zone 35. In other words, at the outlet of the holes 38, the fuel is fed firstly through the portion 41 and then through the portion 42, which has a through cross-section smaller than a through cross-section of the said portion 41.

The variant shown in Figures 4 and 5 differs from that shown in the preceding figures in that, in it, the valve body 31 is incorporated in the head-piece 10 and made as one piece with the said head-piece 10 and in that the axes 39 of the holes 38 are inclined with respect to the axis 9.

In this case also, at the outlet of the holes 38, the fuel is fed firstly though the portion 41 and then through the portion 42 and finally into the cylinder 14.

The pumping unit 1 has a number of advantages mainly resulting from the fact the configuration of the intake chamber 40 is such that: the cavitation affecting the fuel exiting from the cylinder 14 during the delivery stroke of the piston 15 is concentrated in the wider portion 41; cavitation is prevented from being concentrated in the sealing zone 35; wear of the valve body 31 and the closing member 34 is avoided in the zone 35; and correct fluid-tight engagement between the valve body 31 and the closing member 31 is ensured when the closing member 34 is arranged in its closed position.