Title

PUMP UNIT FOR FEEDING FUEL, PREFERABLY DIESEL, TO AN INTERNAL-

COMBUSTION ENGINE

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

In particular, the present invention relates to a pump unit including a high- pressure pump, for example a reciprocating pump, that is designed to feed fuel to an internal-combustion engine; a pre-feed pump, for example a gear pump, that is designed to feed the fuel from a containment tank to the reciprocating pump; and a hydraulic circuit that is designed to connect the containment tank, the pre feed pump, the high-pressure pump and the internal-combustion engine together.

In this case, the reciprocating pump comprises a pump casing, at least two cylinders formed in the pump casing and engaged slidingly by respective pistons, and a drive device for moving the pistons along the related cylinders with an alternating rectilinear motion including a suction stroke for drawing fuel into the cylinders and a delivery stroke for delivering fuel to the internal-combustion engine. Each cylinder is associated with a suction valve for drawing fuel into the cylinder and a delivery valve for delivering fuel to the internal-combustion engine.

The drive device is designed to simultaneously move one piston along the suction stroke and the other piston along the delivery stroke.

The hydraulic circuit includes a first branch connecting the containment tank to the gear pump, a second branch connecting the gear pump to the reciprocating pump, and a third branch connecting the reciprocating pump to the internal-combustion engine.

The second branch has a feed manifold and, for each cylinder, a respective suction line connecting the feed manifold to the cylinder.

In general, the hydraulic circuit also includes a dosing solenoid valve mounted alongside the feed manifold to selectively control the instantaneous flow rate of fuel fed to the reciprocating pump as a function of the values of a plurality of operating parameters of the internal-combustion engine.

The dosing solenoid valve includes a valve casing mounted on the feed manifold and a stopper engaged slidingly in the valve casing to move between an open position and a closed position of the dosing solenoid valve.

When in use, the delivery stroke of each piston commands the related suction valve to close. During closure of each suction valve, some of the fuel compressed by the related piston leaks out of the related cylinder, firstly along the related suction line and subsequently either along the suction line of the other suction valve or along the feed manifold. Known pump units of the type described above have some drawbacks, primarily related to the fact that: the pressure waves generated along the suction line of each cylinder by the fuel leaks from the other cylinder encourage the opening, and therefore further delay the closing, of the related suction valve, amplifying the phenomenon described above; and the pressure waves generated along the feed manifold by the fuel leaks from the two cylinders encourage the opening of the stopper of the dosing solenoid valve, thereby compromising the supply of fuel at the correct flow rate to the reciprocating pump and therefore to the internal-combustion engine.

The present invention is intended to provide a pump unit for feeding fuel, preferably diesel, to an internal-combustion engine that does not suffer from the aforementioned drawbacks and that is simple and inexpensive to implement.

According to the present invention, a pump unit for feeding fuel, preferably diesel, to an internal-combustion engine, as claimed in the attached claims, is provided. The present invention is described below with reference to the attached drawings, which show a non-limiting example embodiment of the invention, in which:

Figure 1 is a hydraulic diagram of a preferred embodiment of the pump unit according to the present invention,

Figure 2 is a schematic cross-section view of a detail of the pump unit in Figure 1, with some elements removed for clarity, and Figure 3 is a perspective view of a detail in Figure 2.

In Figure 1, reference sign 1 denotes, as a whole, a pump unit for feeding fuel, preferably diesel, from a containment tank 2 to an internal-combustion engine 3, in this case a diesel engine.

The engine 3 has a manifold 4 for distributing the fuel, commonly referred to using the term “common rail”, and a plurality of injectors 5 connected to the manifold 4 that are designed to spray the fuel into the related combustion chambers (not shown) of the engine 3.

The pump unit 1 includes a high-pressure pump 6, i.e. a reciprocating pump, to feed the fuel to the engine 3, and a low-pressure or pre-feed pump 7, i.e. a gear pump, for example an electric pump, to feed the fuel from the tank 2 to the pump 6. The pump 6 includes a pump casing 8 and, in this case, two cylinders 9, which are formed in the pump casing 8 and have respective longitudinal axes 10 that are substantially parallel to one another. According to a variant that is not illustrated, there is a different number of cylinders 9, in particular one, and the axes 10 are not parallel to one another.

The cylinders 9 are engaged slidingly by the respective movable pistons 11 by a drive device 12 providing an alternating rectilinear motion including a suction stroke for drawing the fuel into the related cylinders 9 and a delivery stroke delivering the fuel to the engine 3.

The device 12 includes a cam transmission shaft 13 that is seated in a first containment chamber 14 formed in the pump casing 8 and is designed to drive the delivery stroke of the pistons 11.

The device 12 also includes, for each piston 11, a respective spring (not shown) that is seated in a second containment chamber (not shown) that is formed in the pump casing 8 and designed to drive the suction stroke of the piston 11.

Having regard to the foregoing, it should be noted that the shaft 13 is designed to drive the suction stroke of one piston 11 and the delivery stroke of the other piston 11 simultaneously. The pump unit 1 also includes a hydraulic circuit 15, which in turn includes a first branch 16 connecting the tank 2 to the pump 7, a second branch 17 connecting the pump 7 to the pump 6, and a third branch 18 connecting the pump 6 to the manifold

4.

The branch 17 is provided with a filtering device 19 to filter the fuel fed to the cylinders 9 and also has a dosing solenoid valve 20 mounted downstream of the device 19 in a flow direction 21 of the fuel along the branch 17 to selectively control the instantaneous flow rate of fuel fed to the pump 6 as a function of the values of a plurality of operating parameters of the engine 3.

The branch 17 and the branch 18 are connected to each cylinder 9 by a suction valve 22 and a delivery valve 23 respectively.

The circuit 15 also includes a fourth branch 24 that extends between the manifold 4 and the branch 16, enabling the excess fuel flow not required by the injectors 5 to be discharged into the branch 16; and a fifth branch 25, that extends between the branch 17 and the branch 16 and is connected to the branch 17 downstream of the solenoid valve 20 in the direction 21 to feed the fuel drawn through the solenoid valve 20 to the intake of the pump 7 when the solenoid valve 20 is closed.

The circuit 15 also has a sixth branch 26 that extends between the branch 17 and the branch 24, is connected to the branch 17 upstream of the solenoid valve 20 in the direction 21 and is provided with a valve device 27. The device 27 is designed to control the fuel flow used to lubricate the cam transmission shaft 13 and the fuel flow exceeding the fuel supplied through the solenoid valve 20 to the pump casing 8 and the chamber 14. The circuit 15 finally includes a seventh branch 28 feeding the fuel drawn through the pump casing 8 to the branch 26, and therefore the tank 2.

As shown in Figure 2, the branch 17 has a feed manifold 29 and, for each cylinder 9, a respective suction line 30 connecting the manifold 29 to the cylinder 9.

The dosing solenoid valve 20 includes a tubular valve casing 31, which is mounted on the manifold 29 coaxial to a longitudinal axis 32 of the manifold 29, and an annular intake channel 33 that extends about the axis 32 and communicates with the branch 17 to feed fuel through the valve casing 31.

The valve casing 31 is engaged slidingly by a stopper 34, which is cup-shaped, delimited axially by a back wall 35 arranged perpendicularly to the axis 32, and provided with a plurality of connecting holes 36 distributed about the axis 32. The stopper 34 is moveable between an open position, in which the holes 36 are aligned radially with the channel 33, and a closed position, in which the holes 36 are axially offset from the channel 33. The stopper 34 is moved, and normally held, in the open position by a spring 37, and is moved from the open position to the closed position against the action of the spring 37 by an electromagnetic actuator 38 of a known type engaged on the wall 35.

The manifold 29 contains a tubular sleeve 39 that is mounted coaxially with the axis 32, has two axially open free ends, and in this case has three enlarged collars 40 and two narrow sections 41 arranged between the collars 40.

The collars 40 have a diameter that is substantially equal to a diameter of the manifold 29 and are engaged slidingly in the manifold 29. Two of the collars (hereinafter denoted using reference signs 40a and 40b) are arranged on opposite sides of the lines 30 and one of the collars (hereinafter denoted using reference sign 40c) is arranged between the lines 30.

The sections 41 have a diameter that is less than the diameter of the manifold 29, and each of the sections is delimited by a respective side wall 42 that is substantially coaxial with the axis 32.

Each section 41 is provided with a plurality of feed holes 43 that are formed through the respective wall 42, distributed about the axis 32, and have respective longitudinal axes (not shown) that are preferably radial and transverse to the axis 32.

Each hole 43 has a transverse fuel-flow area that is less than a transverse fuel-flow area along the sleeve 39. When in use, the collars 40a, 40b, 40c force the fuel coming from each line 30 during closure of the related suction valve 22 to pass through the holes 43 of the related section 41. Consequently, the pressure waves generated in the manifold 29 by the fuel coming from the lines 30 during closure of the related suction valves 22 are absorbed by passing through the holes 43.

The absorption of the pressure waves generated in the manifold 29 by closure of the valves 22 has some advantages, principally resulting from the fact that the pressure waves in the manifold 29 are relatively reduced and do not compromise the correct dynamic performance of the valves 22 and of the stopper 34 of the dosing solenoid valve 20.

Obviously, the sleeve 39 can be eliminated and replaced, for example, by two screening elements mounted at the intake of the lines 30 and provided with holes 43.