WO2019170370A1

WO2019170370A1 - Pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine

Info

Publication number: WO2019170370A1
Application number: PCT/EP2019/053279
Authority: WO
Inventors: Maurizio Marcolivio; Mauro DE BELLIS; Nello Medoro; Giuseppe MARZILIANO
Original assignee: Robert Bosch Gmbh
Priority date: 2018-03-07
Filing date: 2019-02-11
Publication date: 2019-09-12
Also published as: IT201800003341A1

Abstract

A pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine (3) has a feed duct (29), which connects together a high-pressure pump (6) designed to feed the fuel to the internal combustion engine (3) and a pre-feed pump (7) designed to feed the fuel from a storage tank (2) to the high-pressure pump (6), is provided with a fuel metering electrovalve (20) and has a damping device (39; 46) mounted between the metering electrovalve (20) and the high-pressure pump (6) so as to prevent the pressure waves advancing from the high-pressure pump (6) to said metering electrovalve (20).

Description

Title

PUMPING UNIT FOR FEEDING FUEL, PREFERABLY DIESEL FUEL, TO AN INTERNAL COMBUSTION ENGINE

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

In particular the present invention relates to a pumping unit of the type comprising a high-pressure pump, for example a piston pump, designed to feed the fuel to an internal combustion engine; a pre-feed pump, for example a gear pump, designed to feed the fuel from a storage tank to the piston pump; and a hydraulic circuit for connecting together the storage tank, the pre-feed pump, the high- pressure pump and the internal combustion engine.

In the case in question, the piston pump comprises a pump body; at least two cylinders formed in the pump body and slidably engaged by respective pistons; and an actuating device for displacing the pistons along the associated cylinders with a reciprocating rectilinear movement comprising an intake stroke for drawing the fuel into the cylinders and a delivery stroke for supplying the fuel to the internal combustion engine.

The two cylinders have respective longitudinal axes which are parallel to each other and are each associated with a respective intake valve for drawing the fuel into the cylinder and with a respective delivery valve for supplying the fuel to the internal combustion engine.

The actuating device is configured so as to displace simultaneously a piston with its intake stroke and the other piston with its delivery stroke. The hydraulic circuit comprises a first line for connecting together the storage tank and the gear pump; a second line for connecting together the gear pump and the piston pump; and a third line for connecting together the piston pump and the internal combustion engine.

The second line comprises a feed header and, for each cylinder, a respective intake duct for connecting the feed header to the said cylinder.

Generally, the hydraulic circuit further comprises a metering electrovalve mounted along the feed header of the second line for selectively controlling the instantaneous flow of fuel fed to the piston pump depending on the values of a plurality of operating parameters of the internal combustion engine.

The metering electrovalve comprises a valve body mounted in the feed header and provided with an inlet for entry of the fuel into said metering electrovalve; and a closing member slidably engaged in the valve body so as to move between a position for opening and a position for closing the inlet.

The closing member has a cup-shaped form and is provided with at least one feed hole for allowing the fuel to flow through said closing member.

The metering electrovalve further comprises a spring arranged between the valve body and the closing member so as to displace, and normally keep, the closing member in its open position, and an electromagnetic actuator for displacing the closing member from its open position into its closed position.

The known pumping units of the type described above have a number of drawbacks mainly resulting from the fact that the pressure waves generated in each intake duct by closing of the associated intake valve advance along the feed header and reach the metering electrovalve, cause displacement of the closing member which is independent of the spring and the electromagnetic actuator, adversely affect the correct operation of the closing member and cause an oscillating progression of the fuel flow fed to the piston pump. The object of the present invention is to provide a pumping unit for feeding fuel, preferably diesel fuel, to an internal combustion engine, which does not have the aforementioned drawbacks and which is simple and inexpensive to produce.

According to the present invention a pumping unit for feeding fuel, preferably diesel fuel, to 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 hydraulic diagram of a preferred embodiment of the pumping unit according to the present invention;

Figure 2 is a schematic side view, with parts cross-sectioned, of a detail of the pumping unit of Figure 1;

Figure 3 is a perspective view of a detail of Figure 2; and

Figure 4 is a schematic side view, with parts cross-sectioned, of a variant of the detail of Figure 2.

With reference to Figure 1, 1 denotes in its entirety a pumping unit for feeding fuel, preferably diesel fuel, from a storage tank 2 to an internal combustion engine 3, in the case in question a diesel combustion engine.

The engine 3 comprises a header 4 for distribution of the fuel, commonly known by the term "common rail", and a plurality of injectors 5 connected to the header 4 and designed to atomize the fuel inside associated combustion chambers (not shown) of the said engine 3.

The pumping unit 1 comprises a high-pressure pump 6, namely a piston pump, for feeding the fuel to the engine 3; and a low-pressure or pre-feed pump 7, namely a gear pump, which is for example electrically operated, for feeding the fuel from the tank 2 to the pump 6.

The pump 6 comprises a pump body 8 and, in this case, two cylinders 9, which are formed in the pump body 8 and have respective longitudinal axes 10 substantially parallel to each other.

According to a variant not shown, the number of cylinders 9 is different from two and the axes 10 are not parallel to each other.

The cylinders 9 are slidably engaged by respective pistons 11 movable, under the thrust of an actuating device 12, with an alternating rectilinear movement comprising an intake stroke for drawing the fuel inside the associated cylinders 9 and a delivery stroke for supplying the fuel to the engine 3.

The device 12 comprises a cam transmission shaft 13 which is housed inside a first containing chamber 14 formed in the pump body 8 and is designed to displace the pistons 11 with their delivery stroke.

The device 12 also comprises, for each piston 11, a respective spring (not shown) which is housed inside a second containing chamber (not shown) formed in the pump body 8 and is designed to displace said piston 11 with its intake stroke.

In connection with the above description it should be pointed out that the shaft 13 is configured so as to displace simultaneously a piston 11 with its intake stroke and the other piston 11 with its delivery stroke.

The pumping unit 1 also comprises a hydraulic circuit 15 comprising, in turn, a first line 16 for connecting together the tank 2 and the pump 7; a second line 17 for connecting together the pump 7 and the pump 6; and a third line 18 for connecting together the pump 6 and the header 4. The line 17 is provided with a filtering device 19 for filtering the fuel fed to the cylinders 9 and also has a metering electrovalve 20, mounted downstream of the device 19 in a direction 21 of flow of the fuel along the line 17, for selectively controlling the instantaneous flowrate of the fuel fed to the pump 6 depending on the values of a plurality of operating parameters of the engine 3.

The line 17 and the line 18 are connected to each cylinder 9 by means of an intake valve 22 and a delivery valve 23, respectively.

The circuit 15 also comprises a fourth line 24, which extends between the header 4 and the line 16 and allows the fuel flow which exceeds that needed for the injectors 5 to be discharged into the line 16; and a fifth line 25 which extends between the line 17 and the line 16 and is connected to the line 17 downstream of the electrovalve 20 in the direction 21 for feeding to the inlet of the pump 7 the fuel seeping through the electrovalve 20 when the said electrovalve 20 is closed.

The circuit 15 also has a sixth line 26 which extends between the line 17 and the line 24, is connected to the line 17 upstream of the electrovalve 20 in the direction 21 and is provided with a valve device 27.

The device 27 is configured to control the supply into the pump body 8 and into the chamber 14 of the fuel flow used to lubricate the cam transmission shaft 13 and the fuel flow in excess of that fed through the electrovalve 20.

The circuit 15 comprises, finally, a seventh line 28 for feeding into the line 26 and therefore into the tank 2 the fuel seeping through the pump body 8.

In accordance with that shown in Figure 2, the line 17 comprises a feed header 29 and, for each cylinder 9, a respective intake duct 30 for connecting the header 29 to said cylinder 9.

The metering electrovalve 20 comprises a valve body 31 with a tubular shape, which is mounted in the header 29 coaxially with a longitudinal axis 32 of said header 29 and has an inlet channel 33 with an annular shape, which extends around the axis 32 and communicates with the line 17 so as to feed the fuel through the valve body 31.

The valve body 31 is slidably engaged by a closing member 34 which has a cup shaped form, is axially bounded by an end wall 35 arranged perpendicularly with respect to the axis 32 and is provided with a plurality of connection holes 36 distributed around said axis 32.

The closing member 34 is movable between an open position, in which the holes 36 are radially aligned with the channel 33, and a closed position, in which the holes 36 are axially offset with respect to said channel 33.

The closing member 34 is displaced into, and normally kept in, its open position by a spring 37 and is displaced from its open position into its closed position against the action of the spring 37 by an electromagnetic actuator 38 of the known type engaged with the wall 35.

The spring 37 is arranged between the closing member 34 and a damping device 39 mounted in the header 29 for reflecting at least partially the pressure waves which are generated in each duct 30 by closing of the corresponding valve 22 and which advance along the header 29 towards the electrovalve 20.

With reference to Figures 2 and 3, the device 39 has a cup-shaped form and is bounded by a cylindrical shaped side wall 40 which is axially locked by means of interference inside the valve body 31 and extends coaxially with the axis 32.

The wall 40 projects axially from the valve body 31 and has a free end which is closed by an end wall 41 substantially perpendicular to the axis 32.

The wall 40 has a plurality of feed holes 42 which are distributed around the axis 32 and are formed through the wall 40 transversely with respect to the axis 32.

The wall 41 has a substantially cylindrical shape and has a diameter smaller than the diameter of the header 29. The shape and the size of the wall 41 and the presence of the holes 42 allow the fuel fed through the electrovalve 20 to flow towards the ducts 30.

The wall 41 is bounded axially by a reflecting surface 43 which is situated opposite the electrovalve 20, is in this case substantially flat and perpendicular to the axis 32 and has a smaller area than a through-flow cross-section of the header 29.

The wall 41 also has two substantially flat side faces 44 which are parallel to each other and reflects a quantity of pressure waves proportional to the ratio between the through-flow cross-section of the header 29 and the area of the surface 43.

In other words, the quantity of pressure waves reflected by the surface 43 depends on the ratio between the diameter of the wall 41 and the distance between the faces 44.

The variant shown in Figure 4 differs from that shown in the preceding figures solely in that, in it, the spring 37 is arranged between the closing member 34 and an end-of-travel ring 45 mounted at one end of the valve body 31 coaxially with the axis 32 and the damping device 39 is eliminated and replaced by a damping device 46 mounted between the electrovalve 20 and the ducts 30.

The device 46 has a cup-shaped form and is bounded by a side wall 47 with a cylindrical shape comprising a widened portion 48 axially locked by means of interference inside the header 29 and a narrower portion 49 which has a smaller diameter than the diameter of the header 29 and is provided with a plurality of feed holes 50 which are entirely similar to the holes 42.

The wall 47 has a free end opposite the electrovalve 20 closed axially by an end wall 51 entirely similar to the wall 41.

The damping devices 39, 46 allow the pressure waves which are generated inside each duct 30 by closing of the associated valve 22 and advance along the header 29 towards the electrovalve 20 to be reflected at least partially and ensure correct operation of the closing member 34 of the electrovalve 20, the

displacements of which depend substantially on the action of the spring 37 and the electromagnetic actuator 38.

Claims

1. Pumping unit for feeding fuel, preferably diesel fuel, to the internal

combustion engine (3), the pumping unit comprising a high-pressure pump

(6) for feeding the fuel to an internal combustion engine (3); a pre-feed pump

(7) for feeding the fuel from a storage tank (2) to the high-pressure pump (6); and a hydraulic circuit (15) which connects together the storage tank (2), the pre-feed pump (7), the high-pressure pump (6) and the internal combustion engine (3) and comprises a metering electrovalve (20) mounted along a feed duct (29) for feeding the fuel from the pre-feed pump (7) to the high-pressure pump (6); and being characterized in that the hydraulic circuit (15) further comprises a damping device (39; 46) mounted inside the feed duct (29) between the metering electrovalve (20) and the high-pressure pump (6) so as to prevent the pressure waves advancing from the high-pressure pump (6) to said metering electrovalve (20).

2. Pumping unit according to Claim 1, wherein the high-pressure pump (6) comprises at least one cylinder (9) and, for each cylinder (9), a respective piston (11) slidably engaged inside the cylinder (9) and a respective intake valve (22) movable between a position for closing and a position for opening said cylinder (9); the damping device (39; 46) being mounted between the metering electrovalve (20) and the intake valves (22) so as to reflect at least partially the pressure waves generated by closing of said intake valves (22).

3. Pumping unit according to Claim 1 or 2, wherein the damping device (39; 46) is bounded by a reflecting surface (43) having an area smaller than a through-flow cross-section of the feed duct (29).

4. Pumping unit according to Claim 3, wherein the reflecting surface (43) is substantially flat, in particular perpendicular to a longitudinal axis (32) of the feed duct (29).

5. Pumping unit according to Claim 3 or 4, wherein the reflecting surface (43) has a substantially circular shape with a diameter smaller than a diameter of the feed duct (29).

6. Pumping unit according to any one of the preceding claims, wherein the damping device (39; 46) has a cup-shaped form and is bounded by an end wall (41; 51) and by a side wall (40; 47).

7. Pumping unit according to Claim 6, wherein the end wall (41; 51) has a

substantially cylindrical shape with a diameter smaller than a diameter of the feed duct (29) and is bounded axially by a reflecting surface (43).

8. Pumping unit according to Claim 6 or 7, wherein the end wall (41; 51) also has two substantially flat side faces (44) parallel to each other.

9. Pumping unit according to any one of Claims 6 to 8, wherein the side wall (40; 47) is tubular and is provided with at least one feed hole (42; 50) formed through said side wall (40; 47).

10. Pumping unit according to any one of the preceding claims, wherein the metering electrovalve (20) comprises a valve body (31), which is mounted in the feed duct (29), has an inlet (33) for the fuel in the valve body (31) and is slidably engaged by a closing member (34) movable between a position for opening and a position for closing said inlet (33).

11. Pumping unit according to Claim 10, wherein the metering electrovalve (20) also comprises a spring (37) for displacing, and normally keeping, the closing member (34) in its open position and an electromagnetic actuator (38) for displacing the closing member (34) from its open position into its closed position.

12. Pumping unit according to Claim 11, wherein the damping device (39) is axially locked inside the valve body (31); the spring (37) being arranged between the damping device (39) and the closing member (34).

13. Pumping unit according to Claim 11, wherein the damping device (46) is axially locked inside the feed duct (29); the spring (37) being arranged between the closing member (34) and an end-of-travel ring (45) mounted inside the valve body (31).