EP1123463A1

EP1123463A1 - Fuel injection system for an internal combustion engine

Info

Publication number: EP1123463A1
Application number: EP00958211A
Authority: EP
Inventors: Bernd Mahr; Martin Kropp; Hans-Christoph Magel; Wolfgang Otterbach
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-08-20
Filing date: 2000-08-02
Publication date: 2001-08-16
Anticipated expiration: 2020-08-02
Also published as: US6688277B1; WO2001014727A1; JP2003507651A; ATE292238T1; DE19939423A1; EP1123463B1; DE50009918D1

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

Fuel injection system for an internal combustion engine

State of the art

The invention relates to a fuel injection system for an internal combustion engine according to the preamble of patent claim 1. Such an injection system has become known, for example, from EP 0 711 914 AI.

For a better understanding of the following description, a few terms are first explained in more detail: In a pressure-controlled fuel injection system, the fuel pressure prevailing in the nozzle space of an injector opens a valve body (for example a nozzle needle) against the action of a closing force and thus the injection opening for an injection of the fuel released.

The pressure at which fuel emerges from the nozzle chamber into the cylinder is referred to as the injection pressure. Under a stroke expensive fuel injection system is understood in the context of the invention that the opening and closing of the injection opening of an injector take place with the aid of a displaceable valve member due to the hydraulic interaction of the fuel pressures in a nozzle chamber and in a control chamber. Furthermore, an arrangement is referred to below as central if it is provided for all cylinders together and as local if it is provided for only a single cylinder.

In the pressure-controlled fuel injection system known from EP 0 711 914 A1, fuel is compressed to a first high fuel pressure of approximately 1200 bar with the aid of a high-pressure pump and stored in a first pressure accumulator. Furthermore, the high-pressure fuel is also fed into a second pressure accumulator, in which a second high fuel pressure of approx. 400 bar is maintained by regulating its fuel supply by means of a 2/2-way valve. Via a valve control unit, either the lower or higher fuel pressure is injected into the nozzle area of an injector. passes. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can escape from the nozzle opening.

A disadvantage of this known fuel injection system is that all of the fuel first has to be compressed to the higher pressure level in order to then relieve some of the fuel again to the lower pressure level. In addition, two pressure accumulators are required to store the two fuel pressures. The high-pressure pump, as it is driven by the camshaft of the engine, is in permanent operation, even when the desired pressure has already been built up in the respective pressure accumulator. This permanent high pressure generation and the subsequent relief to the low pressure level stand in the way of better efficiency. When using high-pressure accumulators, the fuel pressure is currently limited to a maximum of approx. 1800 bar for reasons of strength.

A stroke-controlled injection system is known from WO 98/09068, in which two pressure accumulators are also provided for storing the two fuel pressures. A separate high-pressure pump is provided for each pressure accumulator, which is in permanent operation even when the desired pressure has already been built up in the respective pressure accumulator.

Advantages of the invention

To improve the efficiency, a second higher pressure level is generated according to the invention by means of a pressure intensifier. Because this translated print is not in one If the pressure accumulator is stored, a higher injection pressure can be achieved. The two pressure levels can be used to represent a flexible injection such as a boat-shaped injection, pre-injection and post-injection.

Further advantages and advantageous configurations of the subject matter of the invention can be found in the description, the drawing and the claims.

drawing

Various exemplary embodiments of fuel injection systems according to the invention with a hydraulic pressure booster unit, in which fuel is injected with two different fuel pressures, are shown schematically in the drawing and explained in the description below. Show it:

1 shows a first fuel injection system with pressure-controlled injectors and a central pressure translation unit;

Fig. 2 shows a second injection system with pressure-controlled

Injectors and a local pressure translation unit provided for each injector;

3 shows a third injection system with pressure-controlled injectors and in each case one modified local pressure translation unit for each injector; and too ut in

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a valve unit 13 can be connected to the delivery line 5 so that it is pressurized at one end by the fuel in a primary chamber 14. A differential space 15 is relieved of pressure 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 to the higher fuel pressure in accordance with the area ratio of the primary chamber 14 and the pressure chamber 17. The pressure chamber 17 is filled via a check valve 18 provided in the pressure medium 17. The pressure intensifier 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. La, the valve unit 13 is formed upstream of the pressure intensifier 11 and as a 3/2-way valve. The parts 11, 13 and 19 form the central pressure translation unit 6.

The pending at the distribution device 8

Fuel pressure is passed via the pressure line 9 into a nozzle chamber 20 of the injector 10. The injection is pressure-controlled with the aid of a piston-shaped valve member 21 (nozzle needle) which is axially displaceable in a guide bore and whose conical valve sealing surface 22 interacts with a valve seat surface on the injector housing and thus closes the injection openings 23 provided there. Within the nozzle space 20, a pressure surface of the valve element 21 pointing in the opening direction of the valve element 21 is exposed to the pressure prevailing there, the nozzle space 20 continuing through an annular gap between the valve element 21 and the guide bore up to the valve sealing surface 22 of the injector 10. Through the im Pressure prevailing in the nozzle chamber 20, the valve member 21 sealing the injection openings 23 is opened against the action of a closing force (closing spring 24), the spring chamber 25 being relieved of pressure by means of a leakage line 26. Behind the distributor device 8, a check valve arrangement 27 is provided for each injector 10, which allows the fuel in the direction of the injector 10 through a first check valve 28 and the return flow of fuel from the injector 10 by means of a throttle 29 and a second check valve 30 to relieve the Allows distribution device 8 and for pressure reduction.

A pre-injection with the lower fuel pressure takes place when the valve unit 13 is de-energized by energizing the 2/2-way valve 7. By energizing the valve unit 13 as well, the main injection then takes place with the higher fuel pressure. For post-injection with the lower fuel pressure, the valve unit 13 is switched back to the de-energized state. If the primary chamber 14 is connected to the inlet of the high-pressure pump 2 with the aid of the valve unit 13 when the 2/2-way valve 7 is not energized, the pressure medium 12 is reset and the pressure chamber 17 is refilled, which is supplied to the delivery line 5 via the check valve 18 connected. Due to the pressure conditions in the primary chamber 14 and in the pressure chamber 17, the check valve 18 opens, so that the pressure chamber 17 is under the fuel pressure of the high-pressure pump 2 and the pressure medium 12 is hydraulically returned to its starting position.

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Control room 65 limited. From the pressure line 9, the control chamber 65 has a fuel inlet with a first throttle 66 and a fuel outlet to a pressure relief line 67 with a second throttle 68, which can be controlled for leakage 70 by a 2/2-way valve 69. The pressure piece 63 is pressurized in the closing direction by the pressure in the control chamber 65. Fuel under the lower or higher fuel pressure constantly fills the nozzle chamber 20 and the control chamber 65. When the 2/2-way valve 69 is actuated (opened), the pressure in the control chamber 65 can be reduced, so that the opening direction is subsequently increased the valve member 21 pressure force in the nozzle chamber 20 exceeds the pressure force acting on the valve member 21 in the closing direction. The valve sealing surface 22 lifts off the valve seat surface and fuel is injected. The pressure relief process of the control chamber 65 and thus the stroke control of the valve member 21 can be influenced by the dimensioning of the two throttles 66 and 68. The end of the injection is initiated by renewed actuation (closing) of the 2/2-way valve 69, which decouples the control chamber 65 from the leakage line 70 again, so that a pressure builds up again in the control chamber 65, which presses the pressure piece 63 in the closing direction can move. The switchover of the fuel to either the lower or the higher fuel pressure takes place for each injector 61 in the local pressure translation unit 53 through the valve unit 55. The pressure translation unit 53 can either be arranged inside the injector housing (FIG. 4a) or outside (FIG. 4b).

In a fuel injection system 1 for an internal combustion engine, in which fuel with at least two different fuel pressures via injectors 10 in o in

Claims

claims

1. fuel injection system (1; 40; 50; 60) for an internal combustion engine, in which fuel can be injected into the combustion chamber of the internal combustion engine with at least two different fuel pressures via injectors (10; 61),

characterized,

that a hydraulic pressure intensifier (11; 42; 54) is provided in parallel to a bypass line (19; 45; 58) for generating the higher fuel pressure, the pressure intensifier (11; 42; 54) via a valve unit (13; 13a; 44; 55) can be activated and deactivated.

2. Fuel injection system according to claim 1, characterized in that the bypass line (19; 45; 58) is closed when the pressure intensifier (11; 42; 54) is activated.

3. Fuel injection system according to claim 1 or 2, characterized in that the valve unit (13; 44;

55) is arranged in front of the pressure intensifier (11; 42; 54).

4. Fuel injection system according to claim 1 or 2, characterized in that the valve unit (13a) is arranged after the pressure intensifier (11).

Fuel injection system according to one of claims 1 to 4, characterized in that the pressure intensifier (11) is provided centrally for all injectors (10).

Fuel injection system according to one of Claims 1 to 4, characterized in that the pressure intensifier (42; 54) is provided locally locally for each injector (10; 61).

Fuel injection system according to one of the preceding claims, characterized in that at least one central pressure accumulator (51) is provided for storing the lower fuel pressure.

8. Fuel injection system according to one of the preceding claims, characterized in that a central distributor device (8) is provided for distributing the fuel pressure to the individual injectors (10; 61).

9. Fuel injection system according to one of the preceding claims, characterized in that the injectors (10) are designed for pressure control.

10. Fuel injection system according to one of the preceding claims, characterized in that the injectors (61) are designed for stroke control.