Title

ROLLER CAM FOLLOWER FOR A FUEL PUMP ASSEMBLY AND PUMP ASSEMBLY COMPRISING SUCH A ROLLER CAW FOLLOWER

The present invention relates to a roller cam follower for a pump assembly for supplying fuel, preferably diesel, to an internal combustion engine. The present invention also relates to a pump assembly for supplying fuel, preferably diesel, to an internal combustion engine in which said pump assembly comprises such a roller cam follower.

In the prior art, a pump assembly for supplying fuel, preferably diesel, to an internal combustion engine comprises a cylinder head inside which is formed at least one cylinder for housing an associated sliding pumping piston. One end of the pumping piston, in particular the internal end with respect to the pump assembly, is known as the piston foot and is coupled to a cam shaft having an axis orthogonal to the axis of the cylinder. A special spring is provided for keeping the piston foot pressed against the cam shaft. The cylinder head in which the cylinder is formed may therefore be housed in a pump body which contains the cam shaft, or is directly made as a single piece with said pump body. Because of the geometry of the cam, the rotation of the shaft imparts to the piston an alternating movement inside the cylinder. In particular, the piston travels along an intake path, in which it descends towards the axis of the cam shaft and draws fuel into the cylinder, and a compression path in which it moves away from the axis of the cam shaft and compresses the fuel trapped inside the cylinder. The portion of the cylinder where compression takes place is known as the compression chamber, in which the end of the piston referred to as the piston head acts. Generally, the fuel is supplied to the cylinder through an intake hole, while the compressed fuel is discharged along a delivery pipe. The external part of the cylinder head for taking in the fuel, which is to be supplied to the cylinder, is known as the intake chamber. Said chamber is supplied by a pipe, known as the intake pipe, and is closed externally by a special cover sealed against the cylinder head. Outside the cylinder head, the delivery pipe is connected to the engine, preferably by means of a common manifold from which a plurality of injectors extends. Suitable valves are provided for regulating the correct flow of fuel from the intake chamber to the cylinder and from the cylinder to the external manifold.

The intake chamber is connected to the cylinder by means of a valve known as the intake valve, usually in the form of a plug with a stem housed over a guide hole made in the cylinder head and axial with the axis A of the cylinder. Said plug has a first mushroom-like end inside the cylinder at the compression chamber, known as the plug foot, and a second end or plug head, outside the cylinder head. The intake valve places the intake chamber selectively in communication with the compression chamber, to supply to the cylinder the fuel taken from the tank by means of a low pressure pump, usually a gear pump.

As described above, the pumping piston comprises an end inside the pump body, or piston foot, which is kept pressed elastically against the cam shaft. In detail, the piston foot is housed in a roller cam follower which is in turn pressed elastically against the cam of the cam shaft. Said roller cam follower comprises a cup-shaped cam follower body with an axis centred on the axis of the cylinder. The piston foot is coupled to the end wall of the cam follower body, while the side walls of the cam follower body contain, at least partially, the spiral spring which has an axis coinciding with the axis of the cylinder and is configured to push the cam follower against the cam. On the side towards the cam shaft, the roller cam follower comprises a roller with an axis orthogonal to the axis of the piston and parallel to the axis of the cam shaft. In line with current practice in the prior art, the roller comprises an internal journal arranged along the axis of the roller parallel to the axis of the cam shaft, with ends coupled directly to the cam follower body. Said journal is not rotatable with respect to the cam follower body and the cam shaft and therefore the roller comprises a sliding bearing centred on the roller axis and coupled to the outer surface of the journal between the ends thereof that are directly coupled to the cam follower body. Said sliding bearing, which thus acts as an outer covering for the journal, is in direct contact with the cam shaft. To prevent friction between the bearing in rotation owing to the rotation of the cam shaft, and the cam follower body, a suitable amount of play or distance is provided between these elements. To be specific, both radial play, i.e. a space between the outer surface of the bearing and the seat that receives the roller, made in the cam follower body, and axial play between the ends of the bearing and the areas where the ends of the journal are coupled to the cam follower body, are provided.

The above configuration has a number of drawbacks. To be specific, the fact that there is axial play between the ends of the bearing and the areas where the journal is coupled to the cam follower body allows relative axial movement with possible impacts that can cause damage to the two components of the cam follower, in particular the cam follower body.

In relation to this prior art, it is an aim of the present invention to provide a roller cam follower and an associated pump assembly that can overcome the above problems found in the prior art.

There is provided, according to the present invention, a pump assembly for supplying fuel to an internal combustion engine; the pump assembly comprising:

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

- a pump body for housing the cylinder head and a cam shaft having an axis of rotation orthogonal to the axis of the cylinder;

- a roller cam follower pressed elastically against the cam shaft.

Said roller cam follower comprises:

- a cup-shaped cam follower body having an axis coinciding with the axis of the cylinder and having an end wall for coupling with the piston and a side wall for coupling with a cylindrical seat formed in the pump body; and

- a roller having an axis parallel to the axis of the cam shaft, the roller being, on the one hand, in contact with the cam shaft and, on the other hand, coupled to the cam follower body on the opposite side of the end wall with respect to the piston.

Further details of a pump assembly suitable for the present invention have been omitted from the above list of components for the sake of simplicity and because they may be considered to be implicit for a person skilled in the art. For example, although it has not been mentioned, it is obvious that the pump assembly comprises an intake valve for controlling the flow of fuel from an intake chamber to a compression chamber, on the outside and on the inside of the cylinder, respectively. Further details will be given in the description of the attached figures, which depict preferred embodiments of the invention.

According to the main aspect of the invention, the roller cam follower comprises at least one bearing coupled, on the one hand, to the roller and, on the other hand, to the cam follower body. As the bearing is directly in contact with the cam follower body, the play required in the prior art between bearing and cam follower body is no longer necessary, thereby preventing relative movement within this play that can result in collisions between the parts, and the associated wear.

Preferably, the roller is reduced substantially to the journal alone, without the sliding bearing provided for in the prior art and created specifically. Said journal is rotatable about its axis parallel to the axis of the cam shaft. The roller cam follower comprises two bearings inserted respectively between the ends of the journal and the cam follower body, while an intermediate portion of the journal between the ends, i.e. the portion in contact with the cam shaft, is housed with play in a recessed seat of the cam follower body.

Preferably, the two bearings are configured to create an isostatic connection at least along the axis of the journal and may take the form of an axial bearing and a radial bearing.

The invention has been described with reference to the pump assembly but it also relates to the roller cam follower alone.

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

- Figure 1 is a flow diagram of a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low pressure pump and a high pressure pump;

- Figure 2 is a schematic sectional view of a high pressure pump; - Figure 3 is a schematic sectional view of a roller cam follower according to the prior art;

- Figure 4 is a schematic sectional view of a roller cam follower according to the present invention.

Figure 1 is a schematic view of an example of a flow diagram of a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low pressure pump and a high pressure pump. In particular, Figure 1 shows a pump assembly 1 comprising:

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

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

- an intake pipe 6 for supplying the fuel from the low pressure pump 4 to the high pressure pump 5;

- high pressure delivery pipes 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 only schematically and comprises a common manifold 12, supplied by the high pressure delivery pipes 13, and a plurality of injectors 14, designed to nebulize and inject the fuel at high pressure into the cylinders (not shown) of the internal combustion engine 3. In Figure 1, the high pressure pump 5 is shown only schematically and comprises two pumping pistons 8, housed in associated cylinders 9 formed in a cylinder head 10 and supplied with fuel at low pressure at intake valves 11. The cylinders 9 are in turn connected to delivery valves 16, for supplying the fuel at high pressure to the engine 3. Figure 1 also schematically shows a cam shaft 15 which imparts to the pistons 8 the alternating movement inside the cylinders 9. Along the intake pipe 6, in particular between the low pressure pump 4 and the intake valves 11, the pump assembly comprises a metering valve 7.

Figure 2 shows a sectional view of a high pressure pump 5 for supplying fuel to an internal combustion engine 3. This high pressure pump 5 is a pump with two pistons 8 that are parallel along the axis Al, and comprises a pump body 17 for housing two cylinder heads 10 inside which are formed the cylinders 9 for the pistons 8. The pump body 17 houses a cam shaft 15 of axis A2 orthogonal to the axis Al of the cylinders. As in the prior art, the foot of each piston 8 is kept pressed by an associated helical spring, which is axial to the axis Al, against a cam of the cam shaft 15. The elastic coupling between the piston foot 8 and the cam shaft 15 is by means of a roller cam follower 19 which, as in the prior art, comprises a cup-shaped cam follower body 20 for receiving the foot of the piston 8 and the spring 18. On the opposite side with respect to the piston 8, the roller cam follower 19 comprises a roller 21 in contact with the cam shaft 15, of axis A3 parallel to the axis A2 of the cam shaft 15. Said cam follower converts the rotary movement of the cam shaft 15 into the alternating translational movement of the piston 8 along the axis Al. As in the prior art, the cam follower body comprises an end wall or disc 22 on which the spring 18 presses, and a cylindrical wall 23 in contact with a corresponding surface of the pump body 17 which defines a cylindrical seat 24 of axis Al formed in the pump body 17.

Figure 3 shows a sectional view of a roller cam follower 19 according to the prior art. The reference signs used to describe this figure based on the prior art will also be used to describe similar components in Figure 4, which shows an embodiment of a cam follower according to the present invention. As shown in Figure 3, the roller 21 is cylindrical along the axis A3 and comprises ends 27 of smaller radius and an intermediate portion 28 connecting the ends 27, of larger radius. The roller of Figure 3 further comprises a sliding bearing 26 that covers the intermediate portion 28, configured to absorb the rotation of the cam shaft without transmitting the rotation either to the journal 25 or to the cam follower body 20. Complementary to the geometry of the roller 21, the cam follower body 20 comprises a seat 29 for receiving the roller 21 below the end wall 22, on the opposite side with respect to the piston 8. This seat 29 thus comprises a recessed area 30 for receiving the intermediate portion 28 of the roller and two side shoulders 31 for receiving the ends 27. As shown, the ends 27 of the journal 25 are in direct contact with the side shoulders 31 of the cam follower body 19. To be specific, neither of these components, i.e. the journal 25 and the cam follower body 20, is subjected to rotation, which is entirely absorbed by the sliding bearing 26. To prevent friction between the rotating bearing 26 and the non-rotating cam follower body 20, there is play both between the outer surface of the bearing 26 and the recessed area 30 of the seat 29, and between the side faces of the bearing, shown in Figure 3 with the reference sign 32, and the shoulders 31 for coupling with the journal 25.

Figure 4 is a sectional view of a roller cam follower according to the present invention. As shown, this cam follower 19 also comprises a journal 21. However, unlike the prior art of Figure 3, the journal 21 of Figure 4 is configured to rotate and be in direct contact with the cam shaft 15, in other words the intermediate portion 28 substantially has a radius equal to the sum of the radii of the journal 25 and the bearing 26 of Figure 3. According to the invention, the coupling with the cam follower body 20 is by means of bearings 33, 34 inserted between the ends 27 of the journal 25 and the shoulders 31. To allow these bearings to be fitted, either the radius of the ends 27 of the journal 25 or the height of the shoulders 31 is reduced. By contrast, in Figure 3, the coupling between the cam follower body 20 and the journal 25 was direct, effectively rendering these bodies rigidly secured to one another. In particular, the bearings 33, 34 of Figure 4 are configured to create an isostatic connection, at least in the axial direction. According to the embodiment shown, this isostatic connection is achieved by providing an axial bearing 33 at one end 27 of the journal 25 and a radial bearing 34 at the other end of the journal 25. Thus, the axial bearing 33 blocks translational movement of the journal 25 along the axis A3, while thermal deformation is however permitted by the radial bearing 34.

It is clear that amendments and changes may be made to the invention described herein while staying within the scope of protection of the attached claims.