Title

PUM P U NIT FOR FEEDI NG FU EL TO AN I NTERNAL COMBUSTION ENGI N E

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

As is known, a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine comprises a head inside which at least one cylinder for housing the associated sliding pumping piston is formed. One end of the pumping piston, in particular the inner end relative to the pump unit, is connected to an actuator, usually a cam shaft which actuates the movement of the piston. A suitable spring is provided for keeping the shaft pressed against the corresponding actuator. With a reciprocating movement along the cylinder, the piston performs an intake stroke, during which fuel is drawn inside the cylinder, and a compression stroke, during which the fuel trapped inside the cylinder is compressed. The portion of the cylinder where compression is performed is called the compression chamber. Generally, feeding into the cylinder is performed through an intake hole, while discharging of the compressed fuel is performed along a transverse hole, or delivery hole. The external part of the head for receiving the fuel which must be fed to the cylinder is called the intake chamber which is closed externally by a suitable plug, or closure, sealingly fastened to the head. Suitable valves are present along the feed or delivery holes for adjusting the correct flow of the fuel. Outside the head, the delivery valve is connected to the engine, preferably by means of a common header provided with a plurality of injectors.

The intake chamber, which is connected to the cylinder by means of the intake valve, communicates with an intake duct for feeding the fuel drawn from the fuel tank by means of a low-pressure pump, usually a gear pump. The pump unit also comprises filtering systems, for example ring filters at the inlet of the intake chamber, for protecting the components of the high-pressure pump from the impurities present in the fuel fed by the low-pressure pump.

Lubrication of the piston sliding inside the cylinder is ensured by means of the fuel itself which seeps between the piston and the cylinder from the compression chamber as far as the base of the cylinder beyond which the piston interacts with the cam shaft. Since this cam shaft is lubricated by an oil bath, the base of the cylinder must be provided with a seal able to prevent contact between the underlying oil and the seeping fuel which has accumulated at the base of the cylinder.

Moreover, this seeping fuel which has accumulated at the base of the cylinder must be periodically removed from the cylinder precisely because its high temperature could damage the seal located precisely at the base of the cylinder.

According to the prior art, the seeping fuel which has accumulated at the base of the cylinder is again fed to the intake chamber. For this purpose, a special channel is formed in the head and connects the intake chamber to the fuel collection chamber at the base of the cylinder.

This known solution described above has a number of limitations, in particular at least two drawbacks. The first drawback consists in the fact that the temperature of the fuel in the intake chamber is raised as a result of mixing with the hot fuel arriving from the collection chamber at the base of the cylinder. This increase in the temperature inside the intake chamber reduces both the efficiency and the reliability of the head and the seal at the base of the cylinder. The second drawback consists in the fact that the pressure peaks present in the intake chamber are propagated as far as the fuel collection chamber at the base of the cylinder with the direct effect of reducing the recirculating efficiency of the fuel. As an indirect effect of this drawback an increase in the temperature at the base of cylinder occurs with possible damage to the seal and the head. Based on this prior art, an object of the present invention is to provide an innovative pump unit able to overcome the aforementioned problems.

According to the present invention a pump unit for feeding fuel, in particular diesel fuel, to an internal combustion engine is provided. This pump unit comprises:

- a head inside which a cylinder for housing a sliding pumping piston is formed along an axis A;

- an intake valve positioned inside an intake hole between an intake chamber and a compression chamber upstream and downstream of the intake hole, respectively;

- a plug pressed against the head in the region of the intake valve for closing the intake chamber;

- an internal discharge channel formed in the head and connected at one end to a chamber for collecting fuel seeping along the cylinder and at the other end to an external discharge channel formed in the plug.

Advantageously, in this way the hot fuel accumulated inside the collection chamber is not discharged into the intake chamber, thus avoiding both overheating inside the intake chamber and transfer of pressure peaks from the intake chamber to the collection chamber. According to an embodiment of the invention the external discharge channel is configured to discharge the fuel outside the pump unit or inside the pump unit upstream of the intake chamber.

Further characteristic features and advantages of the present invention will become clear from the description below of a non-limiting example of embodiment thereof, with reference to the figures of the attached drawings, in which:

- Figure 1 is a schematic cross-sectional view of a portion of a pump unit for feeding fuel to an internal combustion engine according to the present invention; - Figure 2 is a schematic cross-sectional view of the plug for closing the intake chamber of the pump unit shown in Figure 1;

- Figure 3 is a schematic cross-sectional view of the head of the pump unit shown in Figure 1.

With reference to the list of figures indicated above, Figure 1 shows a schematic cross-sectional view of an example of embodiment of a pump unit according to the present invention for feeding fuel to an internal combustion engine. According to this example the pump unit 1 comprises a head 2 inside which a cylinder 3 with an axis A for housing a sliding pumping piston 4 is formed. An intake duct 5 (only partially visible), for feeding the fuel from a tank outside the pump to the cylinder 3, and a delivery duct (not shown), for discharging the compressed fuel from the cylinder 3, are also formed inside the head 2.

An actuator device (not shown), for example a cam shaft, for actuating the reciprocating movement of the piston 4 inside the cylinder 3, is provided at the inner end, or foot, of the piston 4. For this purpose the piston is pressed by means of a spring 6 against the cam shaft. The cam shaft is lubricated by an oil bath. At the opposite end, or head, of the piston 4 the cylinder 3 is provided with an axial hole 7 along the axis A for housing an intake valve 8 which connects the compression chamber 10 of the cylinder 3 to an intake chamber 9 situated on the outside of the head 2 and fed with the fuel via the intake duct 5. The intake valve

8, in this case a stem-like closing member, on one side projects inside the compression chamber 10 and on the other side projects inside the intake chamber

9. On the outside of the head 2, the intake chamber 9 is closed by a plug 11 pressed against the head 2 by a ring nut 12. Both the sealed connection of the plug 11 relative to the head 2 and the connection between the ring nut 12 and the plug 11 are known.

At the inner end of the cylinder 3, the pump unit 1 comprises a seal 13. This seal 13 has the purpose of preventing the downward flow of the fuel which has seeped between the cylinder 3 and piston 4 and therefore defines inside the head 2 a chamber 14 for collecting the seeping fuel. Preferably this collection chamber 14 has an annular form with respect to the axis A.

As can be seen in Figure 1, an internal discharge channel 15 is formed inside the head 2 and extends from the collection chamber 14 to the intake chamber 9. However, the fuel fed into the internal discharge channel 15 from the collection chamber 14 is not discharged into the intake chamber 9, but inside an external discharge channel 16 formed inside the plug 11. This external discharge channel 16 therefore extends from the outer surface of the plug 11 in contact with the head 2 into the intake chamber 9 towards the outside of the plug 11.

Figure 2 shows a cross-sectional view of the plug 11 in Figure 1. As can be seen, the external discharge duct 16 comprises two sections, i.e. an upstream section 16' and downstream section 16", with different cross-sections. The upstream section 16' has a smaller cross-section than that of the respective downstream portion 16". The terms "upstream" and "downstream" relate to the flow of the fuel passing through the ducts and schematically indicated by arrows in Figure 1. According to the example shown in Figure 2, the downstream portion 16" of the external discharge duct 16 extends into associated sleeve portions which extend parallel to the axis A outside the plug 11, namely from its outer surface 19. The upstream portion 16' of the external discharge duct 16 extends inside the plug 11 and continues into an associated sleeve portion which extends inside the head 2 beyond the usual plane of contact of the plug 11 against the head 11. This plane of contact is schematically indicated in Figure 2 by the reference number 20. In other words, the point of contact between the internal channel 15 and external channel 16 is located along the axis A at a height situated more towards the inside of the pump than the inlet of the hole 8 for feeding fuel into the feed chamber. According to the example shown, the point of contact between the internal channel 15 and the external channel 16 is located along the axis A at the same height as or in alignment, perpendicular to the axis A, with the compression chamber 10 or with the inner surface of the cylinder 3 of the stem-like intake valve 8.

Figure 3 shows a cross-sectional view of the head 2 shown in Figure 1. As can be seen, in the region of the intake chamber 9, the head comprises a lowered seat 21 parallel to the axis A and configured to receive the corresponding projection portion of the external discharge duct 16. In particular, the side walls of this lowered seat 21 make lateral contact with the sleeve portion projecting from the plug 11 which defines the projecting portions of the external discharge duct 16. It is clear that the invention described here may be subject to modifications and variations without departing from the scope of the accompanying claims.