EP1123463B1 - Fuel injection system for an internal combustion engine - Google Patents

Abstract

In a fuel injection system for an internal combustion engine, in which fuel at at least two differently high fuel pressures can be injected via injectors into the combustion chamber of the engine, parallel to a bypass line a hydraulic pressure booster is provided for generating the higher fuel pressure; the pressure booster is actuatable and deactuatable via a valve unit. Since the pressure booster is not constantly in operation, and the losses from friction are also reduced, the efficiency is improved.

Description

State of the art

The invention is based on a fuel injection system for an internal combustion engine according to the preamble of the claim 1.

Such an injection system is for example by the DE 41 18 237 A has become known.

For a better understanding of the following description, some terms are first explained in more detail: In a pressure-controlled fuel injection system is controlled by the pressure prevailing in the nozzle chamber of an injector fuel pressure valve body (eg a nozzle needle) against the action of a closing force and thus released the injection port for injection of the fuel. The pressure with which fuel exits the nozzle chamber into the cylinder is referred to as injection pressure. In the context of the invention, a stroke-controlled fuel injection system is understood to mean that the opening and closing of the injection opening of an injector take place by means of a displaceable valve member due to the hydraulic interaction of the fuel pressures in a nozzle space and in a control space. Further, hereinafter, an arrangement will be referred to as central if it is common to all cylinders, and local if provided for only a single cylinder.

In the known from EP 0 711 914 A1 pressure controlled Fuel injection system is using a high pressure pump Fuel to a first high fuel pressure compressed from about 1200 bar and in a first accumulator saved. Furthermore, the under high pressure standing fuel also in a second pressure accumulator promoted in which by regulating its fuel supply by means of a 2/2-way valve, a second high fuel pressure of about 400 bar is maintained. Over a Valve control unit is either the lower or higher Fuel pressure passed into the nozzle chamber of an injector. There is a spring-loaded valve body by the pressure lifted off its valve seat so that fuel can escape from the nozzle opening.

A disadvantage of this known fuel injection system is that first of all the fuel only to the higher Pressure level must be compressed, then one Part of the fuel back to the lower pressure level relieve. In addition, two pressure accumulators are required to store the two fuel pressures. The high pressure pump is because it is driven by the camshaft of the engine is, permanently in the enterprise and also then, if the desired pressure in the respective accumulator already is constructed. This permanent high pressure generation and the subsequent relief to the low pressure level a better efficiency. When using High pressure accumulator is the fuel pressure for strength reasons currently limited to a maximum of about 1800 bar.

From WO 98/09068 is a stroke-controlled injection system known, in which also two pressure accumulator for storage the two fuel pressures are provided. For each Accumulator is provided its own high-pressure pump, which is permanently in operation and even if the desired pressure already built up in the respective accumulator is.

Advantages of the invention

The invention is defined by the features of claim 1. To improve the efficiency is according to the invention a second higher pressure level by means of a pressure booster generated. Because this translated pressure is not in one Pressure accumulator is stored, can be a higher injection pressure be achieved. Both pressure levels can be used for Representation of a flexible injection such as a boat-shaped Injection, pre and post injection used become.

Further advantages and advantageous embodiments of the subject The invention are the description, the drawing and the claims.

drawing

Fig. 1a und 1b

ein erstes, erfindungsgemäßes Kraftstoffeinspritzsystem mit druckgesteuerten Injektoren und einer zentralen Druckübersetzungseinheit;

Fig. 2

ein zweites, nicht erfindungsgemäßes Einspritzsystem mit druckgesteuerten Injektoren und jeweils einer für jeden Injektor vorgesehenen lokalen Druckübersetzungseinheit;

Fig. 3a und 3b

ein drittes, nicht erfindungsgemäßes Einspritzsystem mit druckgesteuerten Injektoren und jeweils einer modifizierten lokalen Druckübersetzungseinheit für jeden Injektor; und

Fig. 4a und 4b

ein viertes, nicht erfindungsgemäßes Einspritzsystem mit hubgesteuerten Injektoren und jeweils der modifizierten lokalen Druckübersetzungseinheit für jeden Injektor.

Various examples of fuel injection systems with a hydraulic pressure booster unit, in which fuel is injected with two different levels of fuel pressure, are shown schematically in the drawing and explained in the following description. Show it:

Fig. 1a and 1b

a first, inventive fuel injection system with pressure-controlled injectors and a central pressure booster unit;

Fig. 2

a second, non-inventive injection system with pressure-controlled injectors and each provided for each injector local pressure booster unit;

Fig. 3a and 3b

a third, not according to the invention injection system with pressure-controlled injectors and in each case a modified local pressure booster unit for each injector; and

Fig. 4a and 4b

a fourth, not inventive injection system with stroke-controlled injectors and each of the modified local pressure booster unit for each injector.

Description of the embodiments

In the illustrated in Fig. 1a first embodiment of a pressure-controlled fuel injection system 1 promotes a high pressure pump 2 fuel 3 from a storage tank 4 via a feed line 5 to a central pressure booster unit 6 at high pressure, which is constructed by energizing a 2/2-way valve 7 , The high-pressure pump 2 can produce a first (lower) fuel pressure of about 300 to about 1000 bar and, for example, be a cam pump with injection adjuster similar to the distributor injection pump known from DE 35 16 867 A1.

If required, an even higher fuel pressure can be generated via the central pressure booster unit 6. By utilizing wave propagation effects, an injection pressure of more than 2000 bar can be realized. The respectively present fuel pressure is then distributed from a central distribution device 8 to a plurality of high-pressure lines 9 corresponding to the number of individual cylinders, which discharge to the individual injectors 10 (injection device) projecting into the combustion chamber of the internal combustion engine to be supplied. In Fig. 1, only one of the injectors 10 is shown in more detail.

The central pressure booster unit 6 comprises a pressure booster 11 with a pressure means 12 in the form of a displaceable piston element, which can be connected at one end to the delivery line 5 by means of a valve unit 13 , so that it is pressurized by the fuel located in a primary chamber 14 at one end. A differential space 15 is depressurized by means of a leakage line 16 , so that the pressure medium 12 can be displaced in the compression direction to reduce the volume of a pressure chamber 17 . As a result, the fuel in the pressure chamber 17 is compressed corresponding to the area ratio of the primary chamber 14 and the pressure chamber 17 to the higher fuel pressure. The filling of the pressure chamber 17 via a pressure medium 17 provided in the check valve 18th The pressure booster 11 can be bypassed by a parallel bypass line 19 , which can be activated or deactivated by means of the valve unit 13. In Fig. 1a , the valve unit 13 is formed in front of the pressure booster 11 and as a 3/2-way valve. The parts 11, 13 and 19 form the central pressure booster unit 6.

The respectively present at the manifold 8 fuel pressure is passed through the pressure line 9 into a nozzle chamber 20 of the injector 10. The injection is pressure-controlled by means of an axially displaceable in a guide bore piston-shaped valve member 21 (nozzle needle), the conical valve sealing surface 22 cooperates with a valve seat surface on the injector and thus closes the injection openings 23 provided there. Within the nozzle chamber 20 a in the opening direction of the valve member 21 facing pressure surface of the valve member 21 is exposed to the pressure prevailing there, wherein the nozzle chamber 20 continues through an annular gap between the valve member 21 and the guide bore to the valve sealing surface 22 of the injector 10. By the pressure prevailing in the nozzle chamber 20 pressure, the injection openings 23 sealing valve member 21 is controlled against the action of a closing force (closing spring 24 ), wherein the spring chamber 25 is depressurized by means of a leakage line 26 . Behind the manifold 8 for each injector 10 each still a check valve assembly 27 is provided which allows the fuel in the direction of the injector 10 via a first check valve 28 and the return of fuel from the injector 10 by means of a throttle 29 and a second check valve 30 to relieve the Distributor 8 and the pressure reduction permits.

A pre-injection with the lower fuel pressure takes place in de-energized valve unit 13 by energizing the 2/2-way valve 7. By energizing also the valve unit 13 then takes the main injection with the higher Fuel pressure. For a post-injection with the deeper Fuel pressure, the valve unit 13 back in switched back to the de-energized state. Will the primary chamber 14 with the help of the valve unit 13 at no-current 2/2-way valve 7 connected to the input of the high pressure pump 2, so the provision of the pressure medium done 12 and the refilling of the pressure chamber 17, over the check valve 18 is connected to the delivery line 5 is. Due to the pressure conditions in the primary chamber 14 and in the pressure chamber 17 opens the check valve 18, so that the pressure chamber 17 under the fuel pressure the high-pressure pump 2 is and the pressure medium 12th hydraulically returned to its original position. To improve the restoring behavior, one or more several springs in the rooms 14, 15 and 17 arranged be.

In Fig. 1b , the valve unit 13a is formed behind the pressure booster 11 and a 2/2-way valve, which is decoupled from the bypass line 19 via a check valve 31 . The parts 11, 13a, 19 and 31 form the central pressure booster unit 6a.

Hereinafter, in the description of the other figures only the differences to the fuel injection system treated according to FIG. 1. Identical or functionally identical Components are designated by the same reference numerals and are not explained in detail.

In the injection system 40 shown in FIG. 2 , the pressure booster unit 41 is not provided centrally but locally for each injector 10 individually. The local pressure booster unit 41, like the central pressure booster unit 6 shown in FIG. 1 a, comprises a pressure booster 42 with a check valve 43 and a valve unit 44 for switching between the pressure booster 42 and the bypass duct 45.

In the injection system 50 shown in FIG. 3 , the high-pressure pump 2 conveys the fuel via the delivery line 5 into a central pressure accumulator 51 (common rail), in which the fuel is stored under a pressure of approximately 300 to approximately 600 bar. Controlled via a central valve unit 52 (eg, a 3/2-way valve), the fuel from the pressure accumulator 51 via the central distribution device 8 is forwarded to the individual pressure-controlled injectors 10. Each injector 10 is associated with a local pressure booster unit 53 with a pressure booster 54 , by means of which, if necessary from the lower fuel pressure of the pressure accumulator 51, a higher fuel pressure can be generated. Via the valve unit 55 (3/2-way valve), the local pressure booster 54, which is constructed analogously to the central pressure booster 11, are activated. The pressure chamber 56 of the local pressure booster 54 is filled with fuel from the pressure accumulator 51, wherein a check valve 57 in a bypass line 58 parallel to the pressure booster 54 prevents the return of compressed fuel back into the pressure accumulator 51. The parts 54, 55, 57 and 58 form the local pressure booster unit 53, which may be either inside the injector housing ( FIG. 3a ) or outside ( FIG. 3b ).

A pilot injection with the lower fuel pressure of the central pressure accumulator 51 takes place with currentless valve unit 55 by energizing the central 3/2-way valve 52. By energizing the valve unit 55 and then the main injection with the higher fuel pressure. For a post-injection with the lower fuel pressure, the valve unit 55 is switched back to the de-energized state. At the end of the injection, the central valve unit 52 is switched back to leakage 59 and thus the manifold 8 and the injector 10 relieved.

From the injection system 50, the injection system 60 shown in Fig. 4 differs by the use of stroke-controlled injectors 61 and the formation of the central valve unit 62 as a 2/2-way valve. Starting from the pressure-controlled injector 10 of FIG. 1 engages in a stroke-controlled injector 61 on the valve member 21 coaxial with the valve spring 23 to a pressure piece 63 , which limits the valve sealing surface 22 remote from the end face 64 a control chamber 65. The control chamber 65 has a fuel inlet from the pressure line 9 with a first throttle 66 and a fuel outlet to a pressure relief line 67 with a second throttle 68, which is controllable by a 2/2-way valve 69 to 70 leakage. About the pressure in the control chamber 65, the pressure piece 63 is pressurized in the closing direction. Under the lower or higher fuel pressure stagnant fuel constantly fills the nozzle chamber 20 and the control chamber 65. Upon actuation (opening) of the 2/2-way valve 69, the pressure in the control chamber 65 can be reduced, so that in the sequence on the opening direction the valve member 21 acting pressure force in the nozzle chamber 20 exceeds the force acting in the closing direction on the valve member 21 pressing force. The valve sealing surface 22 lifts off the valve seat surface and fuel is injected. In this case, the pressure relief process of the control chamber 65 and thus the stroke control of the valve member 21 via the dimensioning of the two throttles 66 and 68 can be influenced. The end of the injection is initiated by renewed actuation (closing) of the 2/2-way valve 69, which decouples the control chamber 65 again from the leakage line 70, so that in the control chamber 65 again a pressure builds up, the pressure piece 63 in the closing direction can move. The switching of the fuel to either the lower or the higher fuel pressure occurs for each injector 61 in the local pressure booster unit 53 through the valve unit 55. The pressure booster unit 53 can be arranged either inside the injector housing ( FIG. 4a ) or outside ( FIG. 4b ).

In a fuel injection system 1 for an internal combustion engine, different with the fuel with at least two high fuel pressures via injectors 10 in the combustion chamber of the internal combustion engine to be injected can, parallel to a bypass line 19 is a hydraulic Pressure booster 11 for generating the higher fuel pressure provided, wherein the pressure booster 11 via a valve unit 13 can be activated and deactivated. Since the intensifier is not permanently in operation and even the losses are reduced by friction, is the Improved efficiency.

Claims (7)

1. Fuel injection system (1) for an internal combustion engine, in which fuel can be injected into the combustion chamber of the internal combustion engine via injectors (10) at at least two different fuel pressures, a hydraulic pressure intensifier (11) for generating the higher fuel pressure being provided in parallel with a bypass line (19) and it being possible to activate and de-activate the pressure intensifier (11) via a valve unit (13; 13a), characterized in that the pressure intensifier (11) is provided centrally for all injectors (10), and in that a central distributor device (8) is provided to distribute the fuel pressure to the individual injectors (10).
2. Fuel injection system according to Claim 1, characterized in that the bypass line (19) is closed when the pressure intensifier (11) is activated.
3. Fuel injection system according to Claim 1 or 2, characterized in that the valve unit (13) is arranged in front of the pressure intensifier (11).
4. Fuel injection system according to Claim 1 or 2, characterized in that the valve unit (13a) is arranged behind the pressure intensifier (11).
5. Fuel injection system according to one of the preceding claims, characterized in that at least one central pressure accumulator is provided for storing the lower fuel pressure.
6. Fuel injection system according to one of the preceding claims, characterized in that the injectors (10) are configured for pressure control.
7. Fuel injection system according to one of the preceding claims, characterized in that the injectors are configured for stroke control.

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