WO2009053364A1

WO2009053364A1 - Fuel injection system with a high-pressure pump lubricated with the fuel, and associated pump unit

Info

Publication number: WO2009053364A1
Application number: PCT/EP2008/064220
Authority: WO
Inventors: Sascha Ambrock; Angelo Forte; Vito Calabrese; Giuseppe Ficarella; Vittorio Caroli; Marco Lamm; Nello Medoro; Antonio Mercurio
Original assignee: Robert Bosch Gmbh
Priority date: 2007-10-26
Filing date: 2008-10-21
Publication date: 2009-04-30
Also published as: ITMI20072066A1

Abstract

The injection system comprises a high-pressure pump (10) which is lubricated with the fuel and fed by a low-pressure pump (9) via a feed line (11). The high-pressure pump (10) comprises a pump body (26) inside which a pumping member (17) is arranged and has a chamber (27) inside which a mechanism (24) for actuating the pumping member (17), provided with a shaft (23), is arranged. The chamber (27) has an inlet opening (41) communicating with the feed line (11) so as to supply into the chamber (27) itself a part of the fuel fed by the low-pressure pump (9) in order to lubricate and cool the actuating mechanism (24). The chamber (27) also has an outlet opening (55) communicating with a line (38) for discharging the excess pumped fuel. A choke (56) is arranged, for example, in the outlet opening (55), said choke being designed to limit the quantity of fuel discharged from the chamber (27) into the discharge line (38). In particular, the low-pressure pump (9) is a mechanical actuating pump synchronized with the shaft (23) of the actuating mechanism (24) of the high-pressure pump (10) and is combined with this pump (10) so as to form a single pump unit (3).

Description

DESCRIPTION

Title

FU EL INJECTION SYSTEM WITH A HIGH-PRESSU RE PUMP LUBRICATED

WITH THE FU EL, AND ASSOCIATED PUMP UNIT

The present invention relates to a fuel injection system for an internal combustion engine with a high-pressure pump lubricated with the fuel and to the associated pump unit.

As is known, in injection systems of the abovementioned type, the high-pressure pump comprises a pump body inside which the pumping members which are actuated by a mechanism enclosed inside a chamber of the pump body are arranged. This mechanism comprises a camshaft which has support bearings and end seals as well as surfaces for frictional contact between the pumping members and the cams, which surfaces are generally lubricated with part of the fuel supplied to the high-pressure pump.

Normally these systems also comprise a low-pressure pump which is designed to supply the fuel to the high-pressure pump via a feed line, and the usual common rail connected to the delivery side of the high-pressure pump in order to receive the pressurized fuel. A fuel discharge line receives the excess fuel discharged from the common rail together with the lubrication fuel discharged from the pump body chamber and the fuel arising from the injectors or from leakages of the pumping members, in particular between the cylinder and piston.

The low-pressure pump, which is generally a gear pump, may be operated independently of the high-pressure pump, for example by an electric motor. Alternatively, the low-pressure pump may be operated mechanically in synchronism with the high-pressure pump. In this latter case, the delivery of the low-pressure pump depends on the number of revolutions of the engine, so that the quantity of lubricating fuel varies considerably. In some cases, the lubricating fuel may flow out too rapidly from the pump body chamber into the discharge line. In this case, the pump body chamber and the ducts connected thereto could be devoid of lubricant and subject to cavitation effects, while the actuating mechanism could be damaged owing to the high degree of friction.

The object of the present invention is to provide a fuel injection system with a high-pressure pump lubricated by the fuel, which is able to ensure adequate lubrication in any operating conditions of the engine and is devoid of the drawbacks of the known systems and can be manufactured in a simple and low- cost manner.

According to the invention, this object is achieved by a fuel-injection system for an internal combustion engine with a high-pressure pump lubricated by the fuel, as defined in Claim 1.

The object of the invention is also achieved by a pump unit comprising a high- pressure pump lubricated with the fuel and a low-pressure pump, as defined by Claim 24.

Further characteristic features and advantages of the present invention will emerge clearly from the following description of a non-limiting example of embodiment provided with reference to the accompanying figures in which:

- Figure 1 is a diagram of a fuel injection system with a high-pressure pump lubricated with the fuel, according to the invention;

- Figure 2 is a cross-sectional view of a detail of the system shown in Figure 1;

- Figure 3 is a detail of the system shown in Figure 1, according to a variant of the invention; and

- Figure 4 is a cross-sectional view of the detail shown in Figure 2, according to the variant of Figure 3. In Figure 1, 1 denotes in its entirety a fuel injection system for an internal combustion engine, which comprises essentially a tank 2 containing fuel to be pumped, a pump unit 3 indicated schematically by means of a polygon shown in dot-dash lines, and a manifold or common rail 4 designed to receive from the pump unit 3 the pressurized fuel for feeding a series of injectors 5 for the cylinders of an internal combustion engine (not shown in the figure). In particular, the pump unit 3 communicates with the tank 2 via a low-pressure intake line 6 along which a filter 7 for separating the water from the intake fuel is arranged. The pump unit 3 also communicates with the common rail 4 via a delivery line 8.

The pump unit 3 comprises a low-pressure pump 9, for example a gear pump, which is able to compress the intake fuel, so as to impart to it a predetermined pressure, for example in the region of 5 bar. The low-pressure pump 9 is designed to supply the fuel thus compressed to a high-pressure pump 10 via a feed line 11 along which another filter 12 is preferably arranged. The high- pressure pump 10 is designed to compress the fuel received to a very high pressure, for example in the region of 1800 bar, so as to supply it via the delivery line 8 to the common rail 4.

In greater detail, the low-pressure pump 9 draws the fuel from the intake line 6 which is provided with a choke 13 calibrated so as to ensure a predetermined throughput of intake fuel. Moreover, the low-pressure pump 9 may be provided with a bypass valve 14 which is designed to allow the fuel to bypass the pump 9 until its pressure upstream of the choke 13 reaches a minimum value, for example in the region of 0.1 bar above atmospheric pressure. Finally, the low- pressure pump 9 is provided with an overpressure valve 16 designed to discharge the excess fuel pumped by it into the intake line 6.

The high-pressure pump 10 comprises at least one pumping member 17 formed by a cylinder 18 inside which a piston 19 slides with a reciprocating movement.

The cylinder 18 communicates with the feed line 11 via an intake valve 21 and communicates with the delivery line 8 via a delivery valve 22. In particular, the high-pressure pump 10 comprises three pumping members 17 arranged radially at 120° with respect to a shaft 23 which forms part of a mechanism for actuating the three pistons 19, denoted generically by 24.

The high-pressure pump 10 also comprises a pump body 26 which is indicated in the diagram of Figure 1 by means of a quadrilateral shown in broken lines. The pump body 26 comprises an internal chamber 27 which houses the actuating mechanism 24 inside it. The pump body 26 is provided with internal ducts 28, which connect the feed line 11 to the three intake valves 21, and other internal ducts 29 which connect the three delivery valves 22 to the delivery line 8.

The actuating mechanism 24 essentially comprises a cam 31 for actuating the three pistons 19, which is fixed onto the shaft 23. The latter is rotatable in a known manner on supports mounted on the pump body 26 and is provided with a seal for closing the chamber 27. The cam 31 is designed to actuate a prismatic ring 32 which has three flat faces 33. Each of the three pistons 19 rests on a corresponding face 33 owing to the action of a compression spring (not shown in the diagram) which is arranged between a seat of the pump body 26 and a so- called cup (also not shown in the diagram). The bottom of the cup makes contact on one side with the corresponding piston 19 and on the other side with the corresponding flat face 33 of the prismatic ring 32 along which it is able to slide transversely during rotation of the cam 31.

In order to control the fuel which must be fed to the high-pressure pump 10, the feed line 11 is provided, between the filter 12 and the internal ducts 28 for feeding the cylinders 18, with a metering solenoid valve 34 which is designed to control the quantity of fuel which must feed the pump 10. In particular, the solenoid valve 34 is opened and closed under the control of an electronic unit 36 depending on the operating conditions of the engine, namely depending on the fuel which the injectors 5 must inject in each case, in order to reduce as far as possible the variations in pressure in the common rail 4. Preferably, the solenoid valve 34 is controlled by the electronic unit 36 via the PWM (pulse width modulation) system. Control may be performed in synchronism with the intake stroke of each piston 19 of the high-pressure pump 10, varying the stroke part during which the fuel may be drawn in. The common rail 4 is provided with a discharge solenoid valve 37 which, when opened, discharges the excess fuel via a discharge line 38 communicating with the tank 2. Each injector 5 comprises a corresponding metering valve 39 (in the diagram only one of them has been shown). Each metering valve 39 is provided with a chamber for hydraulically controlling the injector 5 by means of the same pressurized fuel. The various metering valves 39 of the injectors 5 discharge the fuel along the discharge line 38. The electronic unit 36 controls, depending on the operating conditions of the engine, not only the metering solenoid valve 34, but also the solenoid valve 37 for controlling the pressure of the fuel in the common rail 4. Finally, the electronic unit 36 also controls the metering valves 39 of the injectors 5 (only one of which is shown in the Figure 1) in order to determine the instant and the duration of each injection operation.

As is known, the shaft 23 is rotated by the engine shaft via mechanical means for transmission of the driving power.

The low-pressure pump 9 is mechanically operated in synchronism with the high- pressure pump 10, for example by means of a section of the shaft 23 extending outside the chamber 27.

In particular, the pump body 26 of the high-pressure pump 10 also defines partly the pump body of the low-pressure pump 9.

According to a variant of the pump unit 3, the low-pressure pump 9 is assembled on the pump body 26 of the high-pressure pump 10.

Both variants are particularly compact, but ensure that the delivery of the low- pressure pump 9 depends solely on the running speed of the engine and not on the load conditions of the engine itself.

In order to lubricate the actuating mechanism 24 during operation, the chamber 27 is provided with an inlet opening 41 which communicates with the feed line 11 via a lubricating line 42. The two lines 11 and 42 are connected by means of a connection 43 arranged between the fuel filter 12 and the metering solenoid valve 34, or between the low-pressure pump 9 and the metering solenoid valve 34 in the case where the fuel filter 12 is not present.

A hydraulic circuit, generically denoted by 44, is arranged along the lubricating line 42. According to a preferred embodiment of the pump unit 3 (not shown in the accompanying drawings) the solenoid valve 34 and the hydraulic circuit 44 are contained in the pump body 26.

In particular, the hydraulic circuit 44 comprises a first choke 45 for metering the quantity of fuel to be supplied directly to the chamber 27, and a variable-flow valve 46. The valve 46 is arranged in parallel with the choke 45 and has an inlet 47 connected to the lubricating line 42 via a second choke 48 for modulating the fuel to be supplied to the chamber 27. Finally, the valve 46 is provided with an outlet 49 communicating with the intake line 6 of the low-pressure pump 9.

The chamber 27 of the pump body 26 also has an outlet opening 55 for the fuel from the chamber 27, which communicates with a discharge line 50 and terminates in an outlet 51 of the pump body 26. In turn, the outlet 51 communicates with the discharge line 38 via an outlet union 52. The internal ducts 28 communicate with another internal duct 53 which is provided with a choke 54 and leads into the discharge line 50. The choke 54 has the function of ensuring a metered fuel flow within the hydraulic circuit 28 and in the absence of delivery from the high-pressure pump 10.

In order to slow down or reduce the fuel flowing out of the chamber 27 so as to ensure better lubrication of the mechanism 24, in the region of the outlet 51, means are provided for limiting the quantity of fuel discharged. In the embodiment according to Figure 1, these means consist of a choke 56 with a calibrated diameter. With reference to Figure 2, this choke 56 may be provided inside a bush 57 inserted in any known manner within the discharge line 50 in the region of the outlet opening 55 of the chamber 27. The tests carried out show that, where the pressure of the fuel in the feed line is in the region of 5 bar, the diameter of the choke 56 may range between 0.5 and 2 mm. Preferably this diameter may be chosen between 1.10 and 1.60 mm.

According to the variant shown in Figure 3, the means designed to limit the quantity of discharged fuel consist of a non-return valve 58 with a maximum throughput of 50 litres per hour.

With reference to Figure 4, the valve 58 is kept closed by a compression spring 59 and is inserted along the discharge line 50, in any known manner, at the outlet opening 55 of the chamber 27. The valve 58 is designed to open when the pressure of the fuel inside the chamber 27 is at least 0.4 bar higher than the pressure of the discharge line 50 and therefore the discharge duct 38. This variant is used for those applications with the pressure inside the duct 38 does not exceed about 1.4 bar so as to prevent overpressures inside the chamber 27.

During operation of the injection system 1, the fuel is supplied to the feed line 11 by the low-pressure pump 9 (Figure 1). From the feed line 11 the fuel passes through the metering solenoid valve 34, flows along the internal ducts 28 of the pump body 26 and the intake valves 21 until it reaches the cylinders 18 of the high-pressure pump 10. A part of the fuel inside the line 11, via the line 42, the hydraulic circuit 44 and the inlet opening 41, enters into the chamber 27 so as to lubricate and cool the actuating mechanism 24, including the rotary couplings of the shaft 23 and the friction couplings of the cups of the pistons 19 making contact with the faces 33 of the prismatic ring 31, and the seals between the shaft

23 and the pump body 26.

From the chamber 27, the fuel passes out through the discharge opening 55, the discharge line 50, the outlet 51 and the union 52, into the discharge line 38. However, discharge of the fuel is slowed down by the choke 56 shown in Figures

1 and 2 or by the non-return valve shown in Figures 3 and 4. In this case, it is ensured that the chamber 27 is always full of lubricant and that every small cavity of this chamber 27 is always filled, preventing the formation of fuel vapour pockets and any corrosion due to cavitation effects. The above description clearly highlights the advantages of the injection system 1 compared to the systems of the known art. In particular it is possible to keep the fuel under a certain pressure inside the chamber 27, improving lubrication of the components of the actuating mechanism 24. Moreover, it is ensured that the fuel fills all the spaces inside the chamber 27, preventing the formation of vapour pockets and corrosion due to cavitation.

It is understood that the system described may be subject to various modifications and improvements without departing from the claims. For example, the low-pressure pump 9 may be separate from the high-pressure pump 10. Moreover, the metering solenoid valve 34 and/or the hydraulic circuit 44 may be outside the pump body 26, while the filter 12 along the feed line 11 may be eliminated. The choke 56, or the non-return valve 58, (Figures 2 and 4) may also be arranged in any position along the discharge line 50 of the chamber 27.

Finally, the high-pressure pump 10 may have a number of pumping members 17 other than three, for example two pumping members arranged opposite each other.

Claims

1. Fuel injection system for an internal combustion engine, comprising a high-pressure pump (10) lubricated with the fuel and designed to be fed with the fuel by a low-pressure pump (9) via a feed line (11), the high-pressure pump (10) comprising a pump body (26) inside which at least one pumping member (17) is arranged, the pump body (26) comprising a chamber (27) inside which a mechanism (24) for actuating the pumping member (17) is enclosed, the chamber (27) being provided with an inlet opening (41) and an outlet opening (55), the feed line (11) communicating with the inlet opening (41) of the chamber (27) in order to supply into the chamber (27) a part of the fuel fed by the low- pressure pump (9), the system being characterized in that it comprises means (57, 58) designed to limit the throughput of the fuel discharged from said chamber (27).

2. System according to Claim 1, characterized in that the low-pressure pump (9) is a mechanical actuating pump synchronized with the mechanism (24) for actuating the high-pressure pump (10).

3. System according to Claim 2, characterized in that the low-pressure pump (9) is a gear pump and is actuated by a shaft (23) of the actuating mechanism (24).

4. System according to any one of the preceding claims, characterized in that the pump body (26) of the high-pressure pump (10) defines part of the low- pressure pump (9).

5. System according to any one of Claims 1 to 4, characterized in that the low-pressure pump (9) is assembled together with the pump body (26) of the high-pressure pump (10).

6. System according to any one of the preceding claims, characterized in that said means (56, 58) comprise a first choke (56) arranged along a first discharge line (50) connected to the outlet opening (55) of the chamber (27).

7. System according to Claim 6, characterized in that the first choke (56) is arranged along the first discharge line (50) at the outlet opening (55) of the chamber (27).

8. System according to the Claim 6 or 7, in which the high-pressure pump

(10) comprises at least one radial pumping member (17) and the feed pressure provided by the low-pressure pump (9) is in the region of 5 bar, characterized in that the first choke (56) has a diameter of between about 0.5 mm and about 2 mm.

9. System according to Claim 8, characterized in that the first choke (56) has a diameter of between about 1.10 mm and about 1.60 mm.

10. System according to any one of the preceding Claims 1 to 5, characterized in that the means (56, 58) comprise a non-return valve (58) arranged along a first discharge line (50) connected to the outlet opening (55) of the chamber (27).

11. System according to Claim 10, characterized in that the non-return valve (58) is arranged along the first discharge line (50) at the outlet opening (55) of the chamber (27).

12. System according to Claim 10 or 11, in which the high-pressure pump (10) comprises at least one radial pumping member (17) and the feed pressure provided by the low-pressure pump (9) is in the region of 5 bar, characterized in that the non-return valve (58) has a flowrate in the region of 50 l/h.

13. System according to any one of Claims 10 to 12, characterized in that the non-return valve (58) comprises a spring (59) calibrated so that the non- return valve (58) opens when the pressure of the fuel inside the chamber (27) is about 0.4 bar higher than the pressure inside the first discharge line (50).

14. System according to any one of Claims 6 to 13, characterized in the first discharge line (50) is provided inside the pump body (26) of the high-pressure pump (10).

15. System according to any one of the preceding claims, characterized in that it comprises a common rail (4), which is fed with fuel by the high-pressure pump (10) and discharges the excess fuel by means of a second discharge line

(38) to a tank (2), the outlet opening (55) communicating with the second discharge line (38) by means of the first discharge line (50).

16. System according to Claim 15, characterized in that the low-pressure pump (9) draws fuel from the tank (2) via a second choke (13).

17. System according to any one of the preceding claims, characterized in that a metering solenoid valve (34) is arranged along the feed line (11).

18. System according to Claim 17, characterized in that the pump body (26) comprises the metering solenoid valve (34).

19. System according to Claim 17 or 18, characterized in that the metering solenoid valve (34) is controlled by an electronic unit (36) depending on the operating conditions of the engine so as to meter the fuel feeding the high- pressure pump (10).

20. System according to one of Claims 17 to 19, characterized in that the feed line (11) communicates with the inlet opening (41) via a line (42) connected upstream of the metering solenoid valve (34), the line (42) being provided with a hydraulic circuit (44) for limiting the throughput.

21. System according to Claim 20, characterized in that the hydraulic circuit (44) comprises a variable-flow valve (46) and a third choke (45), which are arranged in parallel.

22. System according to Claim 15 and any one of Claims 17 to 21, characterized in that the metering solenoid valve (34) communicates with the second discharge line (38) via a line (53) inside the pump body (26), along which a fourth choke (54) for ensuring circulation of fuel inside the internal duct (53) is arranged.

23. System according to any one of the preceding claims, characterized in that low-pressure pump (9) is associated with an overpressure valve (16) and a bypass valve (14).

24. Pump unit for a fuel injection system for an internal combustion engine, comprising:

a high-pressure pump (10), which is lubricated with the fuel and comprises a pump body (26) inside which a plurality of pumping members (17) is arranged, the pump body (26) comprising a chamber (27) inside which a mechanism (24) for actuating the pumping members (17) is housed and which is provided with an inlet opening (41) and an outlet opening (55); and

a low-pressure pump (9) which feeds the high-pressure pump (10) with the fuel via a feed line (11), the feed line (11) communicating with the inlet opening (41) of the chamber (27) so as to supply a part of the fuel fed by the low-pressure pump (9) into the chamber (27), the pump unit (3) being characterized in that it comprises means (56, 58) designed to limit the quantity of fuel discharged from the chamber (27).

25. Pump unit according to Claim 24, characterized in that it comprises a discharge line (50) connected to the outlet opening (55), the means (56, 58) being arranged along the discharge line (50).

26. Pump unit according to Claim 24 or 25, characterized in that the low- pressure pump (9) is a mechanical actuating pump synchronized with the mechanism (24) for actuating the high-pressure pump (10).

27. Pump unit according to Claim 26, characterized in that the low-pressure pump (9) is a gear pump and is actuated by a shaft (23) of the mechanism (24) for actuating the high-pressure pump (10).

28. Pump unit according to one of Claims 24 to 27, characterized in that the pump body (26) of the high-pressure pump (10) defines part of the low-pressure pump (9).

29. Pump unit the according to one of Claims 24 to 27, characterized in that the low-pressure pump (9) is assembled together with the pump body (26) of the high-pressure pump (10).