EP2147207B1 - Fuel injection system having pressure boosting system - Google Patents

Abstract

The invention relates to a fuel injection system for an internal combustion engine having a high pressure pump (14), a high pressure accumulator (18), a plurality of fuel injectors (20), a hydraulic pressure booster (10), and having a control valve (26) for actuating the hydraulic pressure booster (10), wherein the hydraulic pressure booster (10) is provided centrally for all fuel injectors (20). The central hydraulic pressure booster (10) is disposed between the high pressure pump (14) and the high pressure accumulator (18).

Description

The invention relates to a fuel injection system with pressure boost for an internal combustion engine.

State of the art

From the EP 1 754 883 A1 A fuel injection system having a first high-pressure compression stage for the fuel, a second high-pressure compression stage in the form of a pressure booster, a pressure booster switching valve, a high-pressure accumulator and a plurality of injectors is already known. In this case, the pressure booster is provided centrally for all injectors and arranged between the first high-pressure compression stage and the high-pressure accumulator. The control chamber of the known pressure booster is connected via a switching valve with a fuel pump.

Another fuel injection system with pressure boosting, in which a central hydraulic pressure booster is provided for all fuel injectors, is from the EP 1 125 046 B1 known. In this case, the fuel delivered by means of a high-pressure pump is fed to a central pressure accumulator (first common rail). The central pressure booster is connected downstream of the central pressure accumulator in the conveying direction of the fuel and for the pressure-boosted fuel to a further pressure accumulator (second common rail), from which several, corresponding to the number of injectors discharge pressure lines to the individual fuel injectors.

Out EP 1 123 463 B1 Another fuel injection system with pressure boosting is known. A central hydraulic pressure booster for all fuel injectors is arranged in a bypass line parallel to a pressure line which leads from the high-pressure pump to a distributor device, which in turn distributes the fuel to the individual fuel injectors. However, the distribution device has no accumulator function. The parallel-connected central pressure booster is connected between the high-pressure pump and distribution device.

The object of the invention is that of the EP 1 754 883 A1 known fuel injection system such that a simplified structure with fewer components or a more compact space in the pressure booster is achieved. This object is achieved in a fuel injection system with pressure boosting for an internal combustion engine having the features of claim 1.

The measures of the subclaims advantageous developments of the invention are possible.

A compact space is advantageously achieved when the central hydraulic pressure booster has a base body in which a hydraulic storage space is formed, and when the hydraulic storage space is connected via a pressure booster inlet directly to the high-pressure pump hydraulically. For this purpose, a high-pressure chamber and a control chamber is formed in the base body and a pressure booster piston guided axially movable The pressure booster piston acts on the high-pressure chamber for pressure boosting and on the control chamber to control the pressure booster. Of the hydraulic storage space is filled directly from the high-pressure pump. The volume of the hydraulic storage space is designed so that the pressure drop is reduced and the pressure oscillations are damped from the pump delivery to a tolerable for the pressure gain level.

It is further provided that from the high-pressure chamber, a first hydraulic connection as a high-pressure discharge to the high-pressure accumulator and a second hydraulic connection leads into the hydraulic storage space that the first hydraulic connection with the high pressure drainage a first check valve and the second hydraulic connection has a second check valve, and that first check valve blocks a return flow from the high-pressure accumulator into the high-pressure chamber and the second non-return valve blocks an inflow of the pressure-intensified fuel from the high-pressure chamber into the hydraulic accumulator space.

The leakage losses that occur on the pressurized control piston on the pressure translator piston can be reduced thereby, if the central hydraulic booster, the pressure booster piston with a first pressure booster piston part with a larger diameter D ₂₁ and with a second booster piston part with a smaller diameter D ₂₂ executed is, is performed with at least one of the pressure booster piston parts in a formed on the body piston guide body. The piston guide body is at least partially surrounded by an annular space, which is part of the hydraulic storage space. As a result, at least one pressure intensifier piston part is also surrounded by the pressure in the hydraulic storage space. By this measure, the guides of the pressure booster piston are acted upon from the outside at the time of pressure amplification by a support pressure, so that the guide game due to the high internal pressure, which prevails within the high-pressure chamber, less dilated. It is most expedient if the high-pressure chamber with its guide gap for the pressure intensifier piston directly adjacent to the hydraulic storage space. As a result, the loss of leakage from the high-pressure chamber into the medium-pressure hydraulic storage space is low, because the medium pressure is the fuel pressure delivered by the high-pressure pump.

At injection pressures below the maximum delivery pressure of the high-pressure pump, the pressure in the storage space of the high-pressure pump via the inlet is further promoted in a first switching position of the switching valve by check valves on the high-pressure flow to the high-pressure accumulator. From there, the fuel reaches the fuel injectors. During this operation, the central pressure booster is not activated, so that the fuel delivered by the high-pressure pump in the bypass operation of the pressure booster reaches the high-pressure accumulator (common rail).

If injection pressures are required which are above the maximum delivery pressure of the high-pressure pump, the central pressure intensifier must be actuated. For this purpose, the switching valve, which is a 3/2-way valve, electrically, hydraulically or pneumatically operated brought into a second switching position. In this second switching position, the control chamber of the pressure booster is connected to the pressure relief via the switching valve with a pressure booster return.

embodiment

With reference to the drawing, the invention will be described below in more detail.

Figur 1

einen Systemaufbau des erfindungsgemäß vorgeschlagenen Kraftstoffeinspritzsystems und

Figur 2

einen prinzipiellen Aufbau eines hydraulischen Druckverstärkers.

Show it:

FIG. 1

a system structure of the present invention proposed fuel injection system and

FIG. 2

a basic structure of a hydraulic pressure booster.

This in FIG. 1 shown fuel injection system comprises a fuel tank 12, from which via a high-pressure pump 14 fuel is conveyed, which is fed to a central hydraulic pressure booster 10. The central pressure booster 10 is connected via a pressure booster inlet 44 on the one hand with the already mentioned high-pressure pump 14 and applied on the other hand a high-pressure accumulator 18 (common rail). In the high-pressure accumulator 18 are in one of the standing under system pressure fuel to be supplied number of fuel injectors corresponding number of connecting lines to fuel injectors 20, which in the illustration FIG. 1 are indicated only schematically. At the combustion chamber end of the fuel injectors fuel under high pressure - indicated by the arrows - injected into the combustion chamber of a self-igniting internal combustion engine. The return side is located at Fuel injector 20 an injector return 22, in which a pressure booster return 24 which is connected to a switching valve 26, opens. Both the pressure booster return 24 and the injector return 22 provide the low pressure side of the fuel injection system as shown in FIG FIG. 1 in which the discarded amount, be it control amount or leakage amount, is returned to the fuel tank 12.

Due to the arrangement of the central pressure booster 16 between the high-pressure pump 14 and the high pressure accumulator 18, the pressure booster 16 per injection cycle of a fuel injector 20 only once with the switching valve 26 to control. As a result, the amount of control or leakage is significantly reduced depending on the number of injections. The high pressure pump 14 has less fuel to deliver and can be made smaller. The pressure booster 16 is designed in its high-pressure delivery to the maximum possible injection quantity of at least one of the fuel injectors 20.

The central pressure booster 16 according to FIG. 2 comprises a base body 30, which may be constructed in one or more parts. In the main body 30, a hydraulic storage space 48 is integrated. The hydraulic storage chamber 48 is acted upon by the high-pressure pump 14 via the pressure booster inlet 44 with fuel. The storage volume of the hydraulic storage chamber 48 is designed so that the pressure drop is reduced and can be pressure vibrations resulting from the promotion of the high-pressure pump 14, damped to an endurable for the pressure amplification measure.

The central pressure amplifier 16 further comprises a pressure booster piston 32. This in turn comprises a first piston portion with a first pressure booster piston part 54, designed in diameter D ₂₁ , and a second piston portion with a second pressure booster piston part 56, designed in diameter D _22nd The pressure gear ratio i of the booster 16 according to the in FIG. 2 illustrated schematic results to: $$\mathrm{i}\mathrm{=}{{\mathrm{D}}_{\mathrm{21}}}^{\mathrm{2}}\mathrm{/}\left({{\mathrm{D}}_{\mathrm{21}}}^{\mathrm{2}}\mathrm{-}{{\mathrm{<figure-callout\; id="22"\; label="D"\; filenames="imgf0001.png"\; state="\{\{state\}\}">D</figure-callout>}}_{\mathrm{22}}}^{\mathrm{2}}\right)$$

The central pressure booster 10 further comprises a high-pressure chamber 50 for pressure boosting or pressure boosting and a control chamber 52 for driving the pressure booster 16. The pressure booster piston 32 is connected to the control chamber with a second pressure surface on the second pressure booster piston part 56 with the smaller diameter D ₂₂ 52 and with a first pressure surface on the first pressure booster piston part 54 with the larger diameter D ₂₁ exposed to the high-pressure chamber 50.

The pressure booster piston 32 is acted upon by a restoring spring 34, which on the other hand is supported on the piston guide body 36 on the one hand and a collar 33 formed on the pressure booster piston part 56 on the other hand. The pressure booster piston 32, the return spring 34 and the piston guide body 36 are in turn arranged in the storage space 48 that surrounds the piston guide body 36 in the region of the guide of the pressure booster piston 32, expediently in the region of the formed with the diameter D ₂₁ first pressure booster piston part 54. By this measure the guides of the pressure booster piston 32 are acted upon from the outside at the time of pressure amplification by a support pressure. This support pressure from the outside causes due to the pressure prevailing in the interior of the pressure booster 16 enlarged guide clearance widened less far, which would otherwise lead to an undesirable outflow of guide leakage, which in turn would adversely affect the hydraulic efficiency of the booster 16.

From the high-pressure chamber 50, a first hydraulic line branches off as a high-pressure drain 46, which extends to the high-pressure accumulator 18 (common rail). In the high pressure drain 46 is a first check valve 40. From the high pressure chamber 50 further extends a second hydraulic line with a second check valve 38, which leads via a filling line 58 into the hydraulic storage chamber 48. The check valve 38 serves as a filling valve. The first check valve 40 blocks a return flow of fuel from the high-pressure accumulator 18 into the high-pressure chamber 50. The second check valve 38 blocks an inflow of the pressure-translated fuel from the high-pressure chamber 50 into the hydraulic accumulator 48. From the second hydraulic line branches off another hydraulic line, which leads to the switching valve 26. A further hydraulic line connects a further connection of the switching valve 26 with the control chamber 52. About these hydraulic lines of the high-pressure chamber 50 and the control chamber 52 is filled starting from the storage space 48 again with fuel, the refilling of the control chamber 52 after the pressure relief on actuation of the switching valve 26 takes place via the further line in the illustrated switching position of the switching valve 26 and also via the filling line 58 starting from the storage space 48.

The return spring 34, which is arranged between the guide body 36 and a step on the pressure booster piston 32, pushes the pressure booster piston 32 in its initial position, so that it rests with a stop limit 42 on the base body 30. The spring force of the return spring 34 is designed so that the pressure booster piston 32 is brought back to the starting position at the stop limit 42 after the pressure boost at a sufficiently high speed.

At injection pressures below the maximum delivery pressure of the high pressure pump 14 is in accordance with a in FIG. 1 and 2 shown the first pressure switch position of the switching valve 26, the pressure of the high-pressure pump 14 via the pressure booster inlet 44 into the storage space 48 and from there via the designed as a check valve high-pressure valve 40 via the high pressure drain 46 to the high-pressure accumulator 18 promoted. From there, the fuel reaches the fuel injectors 20 to be supplied under system pressure. The fuel compressed by the high-pressure pump 14 thus passes directly from the high-pressure pump 14 to the high-pressure accumulator 18 (common rail) in bypass operation, ie the pressure intensifier 16 not active in this operating mode.

In order to achieve injection pressures above the maximum delivery pressure of the high-pressure pump 14, the pressure amplifier 16 is to be controlled. For this purpose, the switching valve 26 is brought electrically, hydraulically or pneumatically in the second switching position. In this switching position of the switching valve 26, the control chamber 52 is connected to the pressure booster return 24. Fuel flows from the pressure-relieved control chamber 52 via the switching valve 26 into the pressure booster return line 24 and from there into the in FIG. 1 Due to the pressure reduction in the control chamber 52, the pressure booster piston 32 is axially moved against the spring force of the return spring 34, so that the first pressure booster piston part 54, formed in the diameter D ₂₁ , presses into the high-pressure chamber 50 and there Pressure increased. The check valve 38 in turn is closed in the direction of the pressure booster return 24. If the pressure in the high-pressure chamber 50 rises above the pressure on the side of the high-pressure outlet 46, the compressed fuel is conveyed further into the high-pressure accumulator 18 (common rail) by the high-pressure valve 40. The high pressure accumulator 18 is thus filled with the increased pressure from the high pressure chamber 50. From there, the fuel injectors 20 are then subjected to the increased fuel pressure, so that the injection takes place via the fuel injectors with the fuel pressure lying above the delivery pressure of the high-pressure pump 14. The pressure in the high-pressure chamber 50 increases until a force equilibrium is again established at the pressure intensifier piston 32.

Upon deactivation of the switching valve 26, the control chamber 52 is hydraulically connected to the storage space 48 again. Due to this hydraulic connection increases Pressure in the control chamber 52 and the pressure booster piston 32 terminates the process of pressure transmission according to the pressure transmission ratio i in the high pressure chamber 50. At the same time, the high pressure valve 40 closes due to the upcoming pressure difference. The spring force of the return spring 34 now presses the pressure booster piston 32 with the stop limit 42 to the main body 30 of the pressure booster 16. During this period fuel is sucked from the storage chamber 48 via the check valve 38 in the high-pressure chamber 50. If the pressure booster piston 32 has reached the limit stop 42, the switching valve 26 can be actuated for renewed pressure transmission. Before reaching the stop limit 42 although a new control is possible, but not meaningful due to the then still undetermined reset position of a first pressure booster piston member 54 and a second pressure booster piston part 56 having pressure booster piston 32.

Claims (6)

1. Fuel injection system for an internal combustion engine, having a high-pressure pump (14), a high-pressure accumulator (18), a multiplicity of fuel injectors (20), a hydraulic pressure booster (10) and having a switching valve (26) for actuating the hydraulic pressure booster (10), wherein the hydraulic pressure booster (10) is provided centrally for all of the fuel injectors (20), wherein the central hydraulic pressure booster (10) is arranged between the high-pressure pump (14) and the high-pressure accumulator (18), wherein the central hydraulic pressure booster (10) has a basic body (30) in which is formed a hydraulic accumulator chamber (48), wherein in the basic body (30) a high-pressure chamber (50) and a control chamber (52) are formed and a pressure booster piston (32) is guided in an axially movable manner, wherein the pressure booster piston (32) acts on the high-pressure chamber (50) for pressure boosting and acts on the control chamber (52) for actuation of the pressure booster (16), and wherein a filling line (58) is provided which branches off from the hydraulic accumulator chamber (48) and via which the control chamber (52) and/or the high-pressure chamber (50) are refilled after the pressure boosting phase, characterized in that the hydraulic accumulator chamber (48) is hydraulically connected to the high-pressure pump (14) directly via a pressure booster inlet line (44).
2. Fuel injection system according to Claim 1, characterized in that, from the high-pressure chamber (50), a first hydraulic connection in the form of a high-pressure outlet line (46) leads to the high-pressure accumulator (18) and a second hydraulic connection leads into the hydraulic accumulator chamber (48), in that the first hydraulic connection with the high-pressure outlet line (46) has a first check valve (40) and the second hydraulic connection has a second check valve (38), and in that the first check valve (40) blocks a return flow from the high-pressure accumulator (18) into the high-pressure chamber (50) and the second check valve (38) blocks a flow of the pressure-boosted fuel from the high-pressure chamber (50) into the hydraulic accumulator chamber (48).
3. Fuel injection system according to Claim 1, characterized in that the switching valve (26) is assigned, in the basic body (30), to the central hydraulic pressure booster (10).
4. Fuel injection system according to Claim 1, characterized in that the pressure booster piston (32) is formed with a first pressure booster piston part (54) of relatively large diameter D₂₁ and with a second pressure booster piston part (56) of relatively small diameter D₂₂, in that the basic body (30) has a piston guide body (36) for at least one of the pressure booster piston parts (54, 56), and in that the piston guide body (36) is at least partially surrounded by an annular chamber which is part of the hydraulic accumulator chamber (48).
5. Fuel injection system according to one of the preceding claims, characterized in that the pressure booster (16) is inactive at pressures below the maximum delivery pressure of the high-pressure pump (14), and the high-pressure accumulator (18) is charged with the maximum delivery pressure of the high-pressure pump (14) via the accumulator volume (48), the check valves (38, 40) and a high-pressure inlet line (46).
6. Fuel injection system according to one of the preceding claims, characterized in that, when pressures higher than the maximum delivery pressure of the high-pressure pump (14) are delivered, the pressure booster (16) is activated and the control chamber (52) thereof is connected via the switching valve (26) to a pressure booster return line (24) for a release of pressure.

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