Title

PUMP UNIT FOR SUPPLYING FUEL TO AN INTERNAL COMBUSTION

ENGINE

Technical field

The technical field to which the present invention relates is that of pumps, par ticularly high-pressure pumps configured for supplying fuel, preferably diesel oil, to internal combustion engines. In this context, the present invention will tackle the problem of ensuring the correct lubrication of some components regardless of the position or orientation in space of the pump during operation.

Prior Art

As is known, a pump unit for supplying fuel, preferably diesel oil, to an internal combustion engine comprises a head in which at least one cylinder is formed for housing a corresponding sliding pump piston. One end of the pump piston, par ticularly the inner end with respect to the pump unit, known as the “foot” of the piston, is coupled to a camshaft whose axis is orthogonal to the axis of the cylin der. A suitable spring is provided to keep the piston foot pressed against the camshaft. The head in which the cylinder is formed may be housed in a pump body containing the seat for the camshaft, or is made directly in one piece with said pump body. A suitable bearing interposed between the shaft and the pump body is provided at each end of the shaft, to allow the shaft to rotate. At least one flange is also provided for securing the shaft in its seat. As a result of the geome try of the cam, the rotation of the shaft imparts a reciprocating motion to the pis ton in the cylinder. In particular, the piston performs a suction stroke, in which it descends towards the axis of the camshaft and draws fuel into the cylinder, and a compression stroke, in which it moves away from the axis of the camshaft and compresses the fuel trapped in the cylinder. The portion of the cylinder where compression takes place is called the compression chamber, in which the end of the piston known as the piston head acts. The cylinder is usually supplied with fuel through a suction hole, while the compressed fuel is discharged along a de livery conduit. The outer part of the head for collecting the fuel to be supplied to the cylinder is called the suction chamber. This chamber is supplied by a conduit called the suction conduit, and is closed from the outside by a suitable plug fas tened in a sealed way, with a nut for example, against the head. Outside the head, the delivery conduit is connected to the engine, preferably by means of a common manifold from which a plurality of injectors extend.

Suitable valves are provided for regulating the correct flow of the fuel from the suction chamber to the cylinder and from the cylinder to the external manifold.

The suction chamber is connected to the cylinder by means of a valve called the suction valve, usually in the form of a shutter with a stem housed through a guide hole which is formed in the head, and which is axial to the axis A of the cylinder. This shutter has a first mushroom-shaped end, known as the foot of the shutter, inside the cylinder at the position of the compression chamber, and a second end, or head, of the shutter outside the valve head. The suction valve selectively puts the suction chamber into communication with the compression chamber in order to supply the cylinder with the fuel drawn from the tank by means of a low- pressure pump, usually of the gear type.

As described above, the pump piston has one end that is farther inside the pump body, known as the “foot” of the piston, this end being kept pressed in a sprung manner against the camshaft. In detail, the piston foot is housed in a cup-shaped body, known as a roller tappet, which in turn is pressed in a sprung manner against the cam of the camshaft. This roller tappet comprises a cup-shaped tap pet body having an axis centred on the axis of the cylinder. Internally, the bottom of the tappet body is coupled to the foot of the piston, while the lateral walls of the tappet body at least partially contain the coil spring, whose axis coincides with the axis of the cylinder, and which is configured for pushing the tappet against the cam. Externally, the walls face corresponding portions of the pump body and slide along the latter. At the end which is opposite the bottom of the cup, and which faces the camshaft, the roller tappet comprises a roller having an axis that is orthogonal to the piston axis and parallel to the camshaft axis. In this configuration, the pump body forms within itself a chamber for housing the camshaft, particularly for the portion of the shaft having the cams that drive the pistons. This chamber, known as the cam chamber, is therefore delimited as fol lows. Along the shaft axis, it is delimited at opposite ends by the bearings sup porting the shaft itself, while, along the direction circumferential to that axis, it is delimited by the pump body and, locally, by the tappets that house the feet of the pistons. In order to maintain correct lubrication and cooling of the moving compo nents, particularly the bearings and tappets, the cam chamber is usually of the oil bath type.

The axis of the camshaft may be arranged in different orientations in space, ac cording to the different operating or mounting configurations of the pump unit in the corresponding engine assembly. The shaft axis is usually horizontal, that is to say orthogonal to the direction of gravity. In this configuration, there is no special area for oil accumulation on the bottom of the cam chamber, and the rotation of the shaft takes place spontaneously with the correct lubrication, that is to say with the correct distribution of the oil throughout the chamber, although, due to gravity, the oil would tend to accumulate in the lower portion of the chamber only. In this configuration, therefore, the correct lubrication of the bearings supporting the shaft and of the tappets supporting the feet of the pistons is ensured. Unfortu nately, this lubrication is not optimal if the camshaft axis is not horizontal, but in clined, so as to have a first lowered end and a second raised end. In this configu ration, the oil accumulates by gravity at the lowered end, leaving the other end substantially dry. Consequently, the rotation of the shaft cannot ensure correct lubrication (oil distribution) throughout the cam chamber. The area at the raised end is less lubricated, leading to a greater risk of damage to the corresponding bearing and of the nearby tappet.

Description of the invention

In view of this prior art, there is at present a need to provide a novel and innova tive solution in which, in a special pump unit to be detailed below, the lubrication of the cam chamber, that is to say the correct distribution of the oil throughout the chamber, is ensured even if the axis of the camshaft is inclined, rather than hori zontal. A pump unit for supplying fuel to an internal combustion engine suitable for being improved according to the present invention is a pump unit of the type compris ing:

- at least one head in which is formed a cylinder having an axis A1 for housing a slidable pump piston;

- a pump body for housing the head and for housing a shaft with at least one cam having an axis of rotation A2 orthogonal to the axis A1 of the cylinder;

- at least one roller tappet pressed in a sprung manner against the camshaft, for housing one end of the piston.

The structure and operation of a pump of this type are well-known to those skilled in the art, and further details may therefore be omitted without creating problems of clarity as regards the implementation of the invention. In such a structure, the seat housing the camshaft inside the pump body is known as the “cam chamber”, and is a chamber delimited axially by the two bearings interposed between the ends of the shaft and the pump body, and along the circumferential direction by the pump body and the tappet. This cam chamber is of the oil bath type; in fact, the bearings and the tappets, as is known, all require lubrication. As indicated in the description of the prior art, it is possible that the axis of the camshaft may be inclined in use, so that the oil accumulates by gravity in only one area of the chamber, exposing the remainder, that is to say the moving parts present therein, to damage or overheating due to insufficient lubrication. According to the general aspect of the present invention, in order to overcome this problem the pump unit comprises at least one filling valve, connected at one end to an oil supply circuit and at the other end to the cam chamber, wherein this valve is configured for se lectively opening to feed oil into the chamber when the condition of an inclined shaft and the accumulation of oil in only one portion of the chamber is present. Thus extra oil is introduced into the chamber when required, so that it also reaches the areas that would otherwise be dry and exposed to damage.

Preferably, the parameter that is measured to control the opening of the valve, and the consequent flow of oil, is the pressure in the chamber, or rather the pres sure across the valve. For example, the filling valve may be configured for open ing selectively to feed oil into the chamber when a pressure below a threshold value acts on the chamber end of the filling valve. Preferably, the filling valve is housed in the pump body near a bearing.

Preferably, a plurality of filling valves, housed in the pump body near a bearing, are provided.

Preferably, a plurality of filling valves, housed in the pump body near both bear ings, are provided.

According to one embodiment, at least one sensor for monitoring the pressure in the cam chamber is provided, and a control unit is provided for receiving the val ue measured by the sensor and is configured for causing the valve to open if the measured pressure value is below a threshold value.

According to one embodiment, the valve comprises a spring configured for forc ing the filling valve to open and for mechanically enabling the opening of the fill ing valve when a pressure below a threshold value, that is to say a force not ca pable of overcoming the force of the spring, acts on the chamber end of the filling valve.

Description of an embodiment of the invention

Further characteristics and advantages of the present invention will be made clear by the following description of a non-limiting example of embodiment of the invention, with reference to the attached drawings, in which:

- Figure 1 is a simplified view of a hydraulic circuit of a pump unit for supplying fuel, preferably diesel oil, from a tank to an internal combustion engine, in which a low-pressure pump and a high-pressure pump are present in series;

- Figure 2 is a schematic illustration of a high-pressure pump according to the prior art, having two pump pistons in line, driven by a common camshaft;

- Figure 3 shows the pump of Figure 2, with an indication of the distribution of the oil in the cam chamber in a first operating configuration;

- Figure 4 shows the pump of Figure 2, with an indication of the distribution of the oil in the cam chamber in a second operating configuration, in which the distribu tion of the oil throughout the cam chamber is not ensured; - Figure 5 shows pump according to the present invention in the second operat ing configuration in which, as a result of the present invention, the distribution of the oil is ensured throughout the cam chamber.

With reference to the figures, Figure 1 is a schematic view of an example of a hydraulic circuit of a pump unit configured for supplying fuel, preferably diesel oil, from a tank to an internal combustion engine. In this pump unit, a low-pressure pump and a high-pressure pump are present in series. In particular, Figure 1 shows a pump unit 1 comprising:

- a low-pressure pump 4 configured for drawing fuel from a tank 2;

- a high-pressure pump 5 supplied by the low-pressure pump 4;

- a suction conduit 6 for supplying the fuel from the low-pressure pump 4 to the high-pressure pump 5;

- a delivery conduit 13 for supplying the fuel from the high-pressure pump 5 to the internal combustion engine 3.

In this example, the internal combustion engine 3 is shown purely in schematic form, and comprises a common manifold 12, supplied by the high-pressure deliv ery conduits 13, and a plurality of injectors 14, configured for atomizing the fuel and injecting it at high pressure into the cylinders (not shown) of the internal combustion engine 3. In Figure 1, the high-pressure pump 5 is shown purely in schematic form, and comprises two pump pistons 8 which are in line, that is to say with parallel axes. These pump pistons 8 are housed in corresponding cylin ders 9 formed in a head 10 and supplied with the fuel at low pressure via suction valves 11. In turn, the cylinders 9 are connected to delivery valves 16 for supply ing the fuel at high pressure to the engine 3. Figure 1 also shows schematically a camshaft 15 which imparts the reciprocating motion to the pistons 8 in the cylin ders 9. Along the suction conduit 6, particularly between the low-pressure pump 4 and the suction valves 11, the pump unit comprises a metering valve 7.

Figure 2 shows a schematic view in partial section of an example of a high- pressure pump 5 of the type shown schematically in Figure 1, for supplying fuel to an internal combustion engine 3. Evidently, the present invention is limited nei ther to the number of pistons shown, nor to their mutual arrangement in space.

As mentioned above, the high-pressure pump 5 shown is a pump with two pis- tons 8 having parallel axes Al, and comprises a pump body 17 for housing two heads 10. A cylinder 9 is formed inside each head for housing a corresponding piston 8. Alternatively, the heads may be made in one piece with the pump body. The pump body 17 houses a camshaft 15 having a axis A2 orthogonal to the axis Al of the cylinders. In a known way, the foot of each piston 8 is kept pressed against a cam 26 of the camshaft 15 by a corresponding coil spring 18, axial to the axis Al. The sprung coupling between the foot of the piston 8 and the cam shaft 15 is mediated by a roller tappet 19 which, as is known, comprises a cup shaped tappet body 20 for receiving the foot of the piston 8 and the spring 18. At the opposite end from the piston 8, the roller tappet 19 comprises a roller 21, in contact with the camshaft 15, having an axis A3 parallel to the axis A2 of the camshaft 15. This roller tappet 19 converts the rotary motion of the camshaft 15 into the reciprocating translational motion of the piston 8 along the axis Al. As is known, the body of the tappet comprises a bottom or plate 22 on which the spring 18 presses internally, and a cylindrical wall 23 in contact with a corresponding surface of the pump body 17 that defines a cylindrical seat 24 with an axis Al formed in the pump body 17. As shown, the pump body forms a seat 27 for hous ing a portion of the camshaft 15, that is to say the portion having the cams 26, which is delimited along the axis A2 at opposite ends by two bearings 25 for sup porting the shaft 15, and radially to the axis A2 by the pump body and by the tap pets 22. Finally, a first end of the shaft 15 is supported by a flange 28 fixed to the pump body 17, while the opposite end is coupled to the low-pressure pump (visi ble in the subsequent figures).

Figure 3 shows the known pump of Figure 2 in a first operating configuration, in which the distribution of the oil in the cam chamber for the lubrication and cooling of some components of the pump is indicated. The same components as those of Figure 2 are present in this Figure 3, and therefore, for the sake of simplicity, not all of the reference numerals present in Figure 2 are shown in Figure 3, and it is only the new specific aspects or elements relevant to the description that are in dicated. As mentioned in the section on the prior art, the pump body 17 compris es a seat for housing the camshaft 15, particularly a seat 27 for the portion of the shaft 15 provided with the cams 27. This seat is known as the cam chamber, and is a chamber limited along the axis A2 by the bearings 25 and along the circum ferential direction by the pump body 17 itself and by the tappets 19 supporting the feet of the pistons. The first operating configuration shown is a configuration in which the axis A2 of the shaft 15 is orthogonal to the direction of gravity G (a reference which is absolute and presents no problems of clarity). In this configu ration, the lubricating and cooling oil introduced into the chamber is uniformly dis tributed throughout the chamber by the rotation of the shaft. There are no local accumulations or areas lacking oil due to gravity, and therefore the lubrication of both the bearings 25 and the tappets 19 is ensured.

Figure 4 shows the pump of Figure 3 in a second operating configuration, in which, according to the prior art, lubrication throughout the cam chamber is not ensured. In this second configuration, the axis A2 of the shaft 15 is no longer hor izontal or orthogonal to the direction G, but is in an inclined position. As a result of this inclination, a first end of the shaft 15 is at a lower level, or a lowered posi tion, while the opposite end is at a higher level, or a raised position. In this con figuration, the oil introduced into the chamber accumulates spontaneously due to gravity in the lowered end of the shaft, leaving the remaining raised part of the chamber lacking in oil. The reference 28 identifies this local accumulation. Con sequently, the rotation of the shaft cannot distribute the oil throughout the cham ber, but only at the lowered bearing and the tappet near it. The moving members in the raised area (bearing and tappet) are therefore unlubricated, and are thus exposed to damage and overheating (shown schematically in Figure 4 by the ref erence D).

Figure 5 shows a pump according to the present invention in the second operat ing configuration described above, in which, as a result of the present invention, lubrication is ensured throughout the cam chamber even when the shaft is in clined. In particular, according to this example of the invention, the pump body is provided with a valve 30 connected at one end to an oil supply circuit 29 and at the other end to the cam chamber 27. This valve 30 may be automatic or con trolled by a suitable sensor, but in all cases it is configured for selectively opening and introducing oil into the chamber when a pressure below a threshold value is created in the chamber at the position of the valve 30. In the example shown, a pressure P acts on the valve 30 from the oil supply circuit end, and a pressure P’, which is greater than P, acts on it from the chamber end. The valve in this exam ple is of the spring type, and opens when the pressure P’ falls below a threshold value and closes when the original pressure P’ is restored. Since the pressure P’ in the chamber falls locally (that is to say, across the valve) only if there is a lack of oil in the area observed, in this case provision is made to inject oil into cham ber until the desired local pressure P’ is restored. In this condition, the amount of oil present in the chamber is greater, and uniformly reaches even the portions at a higher level, thus preventing damage or overheating in this second configura tion also. Clearly, a greater number of valves, and a greater number of sensors if necessary, may be provided to obtain the same result in a plurality of different in clined arrangements of the camshaft.

It is evident that the invention described here may be modified and varied without departure from the scope of protection of the attached claims.