Metering valve for a pump unit for feeding fuel to internal combustion engine and pump unit comprising such a valve

Abstract

A metering valve for a pump unit for feeding fuel from a tank to an internal combustion engine; the metering valve having: a sleeve having an axis A and provided with a first open end for receiving a thruster, a second opposite end provided with an opening for axially discharging the fuel and at least one side opening for feeding fuel; a plug-shaped piston housed slidably along the axis A inside the sleeve, the piston being provided with a closed end having an outer surface in contact with the thruster, an open opposite end and at least one side opening; a plug housed inside the discharge opening of the sleeve and provided with an axial opening; a spring arranged between the plug and the inner surface of the closed end of the sleeve.

Claims

1. A metering valve (7) for a pump unit (1) for feeding fuel from a tank (2) to an internal combustion engine (3); the metering valve (7) comprising: a sleeve (27) having an axis (A) and provided with a first open end for receiving a thruster (21), a second opposite end provided with an opening (35) for axially discharging the fuel and at least one side opening (28) for feeding fuel; a plug-shaped piston (30) slidably housed along the axis A inside the sleeve (27), the piston (30) having a closed end (31) with an outer surface in contact with the thruster (21), an open opposite end and at least one side opening (34); a plug (33) housed inside the discharge opening (35) of the sleeve and provided with an axial opening (38); and a spring (32) arranged between the plug (33) and the inner surface of the closed end (31) of the sleeve; wherein the plug (33) is shaped so that, when housed inside the axial discharge opening (35), at least one lateral flow channel (39) for discharging the fuel is present, wherein the piston (30) has at least one side opening (34) cooperating with the side opening (28) of the sleeve (27) so that, selectively, fuel passes through the side opening (28) of the sleeve (27) and the side opening (34) of the piston (30) and is discharged via the open end of the piston (30), and wherein the plug (33) is provided with an axial through-hole (38) centered on the axis (A).

2. The valve as claimed in claim 1, wherein the plug (33) is shaped so that, when housed inside the axial discharge opening (35) of the sleeve (27), a plurality of lateral flow channels (39) for discharging fuel are present.

3. The valve as claimed in claim 2, wherein the lateral flow channels (39) are axially symmetrical with respect to the axis (A).

4. The valve as claimed in claim 1, wherein the plug (33) comprises an inner face provided with an axial step (37) for seating the spring (32).

5. The valve as claimed in claim 4, wherein the plug (33) comprises a side wall (36) having at least one portion for contact with the axial discharge opening (35) of the sleeve (27) and at least one inset portion (41) having a radius (R2) from the axis (A) smaller than the radius (R1) of the contact portion.

6. The valve as claimed in claim 5, wherein the radius (R2) of the inset portion (41) coincides with the outer radius of the axial step (37).

7. The valve as claimed in claim 1, further comprising a device for electromagnetically actuating the thruster (21).

8. A pump unit (1) for feeding fuel from a tank (2) to an internal combustion engine (3); the pump unit (1) comprising: a low-pressure pump (4) for drawing fuel from the tank (2); a high-pressure pump (5) fed by the low-pressure pump (4) for delivering high-pressure fuel to the engine (3), the high-pressure pump (5) comprising at least one intake valve (11) for feeding fuel into at least one cylinder (9) for housing a pumping piston (8) movable with a reciprocating motion between an intake stroke and a compression stroke; an intake duct (6) which connects the low-pressure pump (4) to the high-pressure pump (5); and a valve (7) according to claim 1, the valve being arranged along the intake duct (6) for controlling the fuel fed to the intake valve (11) by the low-pressure pump (4).

9. A plug (33) for a metering valve (7) of a pump unit (1) for feeding fuel from a tank (2) to an internal combustion engine (3); wherein the metering valve (7) comprises: a sleeve (27) having an axis (A) and provided with a first open end for receiving a thruster (21), a second opposite end provided with an opening (35) for axially discharging the fuel and at least one side opening (28) for feeding fuel; and a plug-shaped piston (30) slidably housed along the axis (A) inside the sleeve (27), the piston (30) having a closed end (31) with an outer surface in contact with the thruster (21), an open opposite end and at least one side opening (34); wherein the plug (33) is shaped so as to be stably housed inside the discharge opening (35) of the sleeve and provided with an axial opening (38); and wherein the plug (33) is shaped so that, when the plug is housed inside the axial discharge opening (35), at least one lateral flow channel (39) for discharging fuel is present wherein the piston (30) has at least one side opening (34) cooperating with the side opening (28) of the sleeve (27) so that, selectively, fuel passes through the side opening (28) of the sleeve (27) and the side opening (34) of the piston (30) and is discharged via the open end of the piston (30), and wherein the plug (33) is provided with an axial through-hole (38) centered on the axis (A).

10. A method for increasing the flowrate of a metering valve (7) of a pump unit (1) for feeding fuel from a tank (2) to an internal combustion engine (3) without modifying the dimensions and the possibility of standardization of the components, the method comprising the steps of: a) providing a valve (7) comprising a sleeve (27) having an axis (A) and provided with a first open end for receiving a thruster (21), a second opposite end provided with an opening (35) for axially discharging the fuel and at least one side opening (28) for feeding fuel; a plug-shaped piston (30) slidably housed along the axis (A) inside the sleeve (27), the piston (30) having a closed end (31) with an outer surface in contact with the thruster (21), an open opposite end and at least one side opening (34); a plug (33) housed inside the discharge opening (35) of the sleeve and provided with an axial opening (38); a spring (32) arranged between the plug (33) and the inner surface of the closed end (31) of the sleeve; the piston (30) having at least one side opening (34) cooperating with the side opening (28) of the sleeve (27) so that, selectively, fuel passes through the side opening (28) of the sleeve (27) and the side opening (34) of the piston (30) and is discharged via the open end of the piston (30); and wherein the plug (33) is provided with an axial through-hole (38) centered on the axis (A); and b) providing the plug (33) with a shape so that, when the plug is housed inside the axial discharge opening (35), at least one lateral flow channel (39) for discharging the fuel is present.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 is a view showing a hydraulic diagram of a pump unit for feeding fuel, preferably diesel fuel, from a tank to an internal combustion engine, in which a low-pressure pump and a high-pressure pump are arranged in series;

(3) FIG. 2 is a schematic cross-sectional view of an example of a metering valve arranged along the circuit shown in FIG. 1 between the low-pressure pump and the high-pressure pump;

(4) FIGS. 3 and 4 show, respectively, a retaining plug according to the prior art for the valve shown in FIG. 2 and engagement thereof inside said valve;

(5) FIGS. 5 and 6 show, respectively, a retaining plug according to the invention for the valve shown in FIG. 2 and engagement thereof inside said valve;

DETAILED DESCRIPTION

(6) FIG. 1 is a schematic view of an example of a pump unit for feeding fuel, preferably diesel fuel, from a tank to an internal combustion engine, in which a low-pressure pump and a high-pressure pump are arranged in series. In particular, FIG. 1 shows a pump unit 1 comprising:

(7) a low-pressure pump 4 for drawing fuel from a tank 2;

(8) a high-pressure pump 5 fed by the low-pressure pump 4;

(9) an intake duct 6 for feeding the fuel from the low-pressure pump 4 to the high-pressure pump 5;

(10) high-pressure delivery ducts 13 for feeding the fuel from the high-pressure pump 5 to the internal combustion engine 3.

(11) In this example the internal combustion engine 3 is shown only in schematic form and comprising a common header 12 fed by the high-pressure delivery ducts 13 and a plurality of injectors 14 configured to atomize and inject the high-pressure fuel into the cylinders of the internal combustion engine 3 (not shown). In FIG. 1 the high-pressure pump 5 is shown only in schematic form and comprises two pumping pistons 8 housed inside associated cylinders 9 formed in a head 10 and fed with the low-pressure fuel at feed valves 11. The cylinders 9 are in turn connected to delivery valves 16 for feeding the high-pressure fuel to the engine 3. FIG. 1 shows moreover in schematic form a cam shaft 15 which imparts the reciprocating movement inside the cylinders 9 to the pistons 8. Along the intake duct 6, in particular between the low-pressure pump 4 and the intake valves 11, the pump unit comprises a metering valve 7. The operating principle of this valve 7 will emerge more clearly from the description of FIG. 2.

(12) In accordance with that shown schematically in FIG. 2, the metering unit 2 is an electric valve, with at least one inlet side which communicates with the delivery of the low-pressure pump and at least one outlet side which communicates with the intake duct for feeding the intake chamber.

(13) The metering unit 7 is flanged on a support body 17 which normally forms part of the high-pressure pump body and comprises an electromagnetic head 18. This electromagnetic head 18 comprises a coil 19 having an axis A inside which a core 20 made of magnetizable material is formed. The core 20 is mounted in an axially slidable manner along the axis A and comprises a thruster 21 coaxial with the axis A. The electromagnetic head 18 comprises furthermore a cup-shaped piece 22 which supports an electrical connector 23 for supplying current to the coil 19. This cup-shaped piece 22 houses a first end 25 of the thruster 21 and is provided with a flange 24 for connecting the valve 7 to the support body 17. The opposite end 26 of the thruster 21 penetrates inside a sleeve 27 which is coaxial with the axis A and is provided with a flange 28′ which extends radially inwards, from the flange 24 of the cup-shaped piece 22, so that the sleeve 27 is locked by the cup-shaped piece 22 against the support body 17. As shown, the sleeve 27 penetrates at least partially inside the support 17. This portion of the sleeve 27 inside the support body 17 is provided with side openings 28 fed with the fuel delivered by the low-pressure pump 4. Special filters 29 are provided opposite these side openings 28. A piston 30 sliding along the axis A is housed inside the sleeve 27. This piston 30 is plug-shaped, namely comprises a cylindrical body with a closed end or top 31 and an open opposite end. The outer surface of the top 31 is pressed in a spring-loaded manner against the thruster 21. As shown in fact, a spring 32 is housed, partly inside the piston having a first end making bearing contact against the inner surface of the piston 30 and a second end bearing against a retaining plug 33 fastened inside the axial discharge opening 35 of the sleeve 27 in a position facing the open end of the piston 30. When current is supplied to the coils 19 a magnetic force is generated and this acts on the thruster 21 so as to overcome the force of the spring 32 and therefore cause displacement of the piston 30 relative to the sleeve 27. The movable piston 30 comprises side windows 34 (only partially visible in FIG. 2) which, during the piston stroke, are selectively arranged opposite the side openings 28 of the sleeve 27. In these conditions the fuel first passes beyond the openings 28 of the sleeve 27 and the windows 34 of the piston 30 and is then discharged via the open end of the piston 30. The particular profile of the windows 34 of the piston 30 is designed such that the fuel flow passing during the downward movement of the said piston 30 is proportional.

(14) FIGS. 3 and 4 and FIGS. 5 and 6 show respectively a retaining plug according to the prior art and according to the invention and the associated connections with the discharge opening 35 of the sleeve 27.

(15) As is known, the retaining plug 33 of the spring 32 has a cylindrical shape and comprises a side wall 36 so as to engage with the discharge opening 35 of the sleeve 27 and comprises in the surface facing the piston 30 a circumferential step 37 centred on the axis A for stably seating the spring 32. In order to allow discharging of the fuel, the retaining plug 33 comprises a through-hole 38 centred on the axis A and having a radius smaller than the step 37. According to the prior art schematically shown in FIGS. 3 and 4, when the plug 33 is inserted inside the discharge opening 35 of the sleeve 27 the side wall 36 is in contact over its entire length with the discharge opening 35 of the sleeve. In this condition the fuel may pass exclusively via the through-hole 38.

(16) FIGS. 5 and 6 show how, according to the present invention, it is possible to increase the flow passing via the discharge opening 35, without modifying this discharge opening 35 nor the dimensions of the through-hole 38.

(17) According to the present invention the side wall 36 is shaped so as to identify a portions 40 making contact with the discharge opening 35 and at least one side opening 39 between the side wall 36 and the discharge opening 35. This side opening 39 is in fact defined by an inset portion 41 having a radius R2 relative to the axis A smaller than the radius R1 of portion 40 making contact with the discharge opening 35. In the example shown three side openings 39 are present, these being formed in the region of three inset portions 41, so as to ensure an axial symmetry able to absorb uniformly the load of the spring 32. The minimum radius of these inset portions 41, which forms the maximum opening 39, coincides with the outer radius of the step 37.

(18) It is clear that the present invention described here may be subject to modifications and variations without departing from the scope of the accompanying claims.