EP1649161A1

EP1649161A1 - Fuel injection system for combustion engines

Info

Publication number: EP1649161A1
Application number: EP04762380A
Authority: EP
Inventors: Holger Rapp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-07-17
Filing date: 2004-07-13
Publication date: 2006-04-26
Also published as: US20060185647A1; CN1823222A; DE10332484A1; KR20060041236A; WO2005010351A1; JP2006511760A

Abstract

The invention relates to a fuel injection system for combustion engines that has a high-pressure part and a low-pressure part. In the high-pressure part, fuel is supplied from a fuel tank to a high-pressure accumulator (5) via a high-pressure pump (4) and a high-pressure line (32). Injectors (7) are supplied from the high-pressure accumulator (5) via high-pressure supply lines (6). In the low-pressure part, the injectors (7) are connected to a low-pressure accumulator (9) via injector return lines (8) whereby, in the low-pressure accumulator (9), a pressure greater than or equal to 50 bar is maintained by a pressure maintaining valve (11). When a pressure inside the low-pressure accumulator (9) exceeds the opening pressure of the pressure maintaining valve (11), the fuel is returned into the fuel tank via a return line (12). The low-pressure accumulator (9) is connected to the high-pressure line (32) of the high-pressure part via an overflow valve (15) and an overflow line (33).

Description

Fuel injection system for ner internal combustion engines

Technical field

Fuel injection systems with high-pressure accumulators are used in self-igniting internal combustion engines. When using piezo-controlled injectors, a return back pressure in the area of the hydraulic coupler is required. The return counter pressure is achieved by connecting the injectors to a low pressure accumulator. To ensure safe operation when starting the internal combustion engine, the low-pressure accumulator must first be filled. State of the art

Injectors controlled with a piezo actuator have much shorter switching times than injectors that are controlled with a solenoid valve or electrohydraulically. To ensure the function of the piezo actuator over the entire speed range, the piezo-controlled injectors require a return counter pressure of around 10 bar in the area of their hydraulic coupler. The return back pressure is achieved in that fuel injection systems equipped with piezo-controlled injectors are equipped with a low pressure accumulator. The low pressure accumulator is closed by a pressure maintaining valve, which acts as a pressure relief valve in the direction from the injector to the tank. In this way, the return quantity of the injectors is backed up to a defined return pressure of approximately 10 bar during operation of the internal combustion engine.

In the direction from the fuel tank to the low-pressure accumulator, the pressure-maintaining valve acts as a check valve with an opening pressure of approximately 0.3 bar. In fuel injection systems ^' with an electric low-pressure pre-feed pump, the discharge side of the pressure control valve is hydraulically connected to the delivery side of the low-pressure pre-feed pump. In this way, the delivery pressure of the low-pressure prefeed pump, which is in the range of 3 to 5 bar, is immediately available to the low-pressure accumulator when the internal combustion engine starts. This ensures that the injectors are supplied even when the low-pressure accumulator is not completely filled with fuel. _, This applies in particular to the case when the low-pressure accumulator was dismantled in the event of service and in particular also to the first start of the fuel injection system in the engine plant. In many cases, however, fuel injection systems without a low-pressure feed pump are also used. With these fuel injection systems, however, there is no possibility of filling the low-pressure accumulator before the internal combustion engine starts.

Presentation of the invention

The injectors of a fuel injection system for self-igniting internal combustion engines are operated either with the aid of piezo actuators, solenoid valves or electrohydraulically. When using injectors that are equipped with a piezo actuator, a return counter pressure of about 10 bar is required to ensure the function over the entire speed range of the internal combustion engine. The return back pressure is achieved by connecting the injectors to a low-pressure accumulator on the return side. The function of the piezo-controlled injectors is guaranteed by the fuel pressure in the low-pressure accumulator, which is closed off by a pressure-maintaining valve. In order to ensure the function of the injectors even when the internal combustion engine starts, it is necessary to fill the low-pressure reservoir before the internal combustion engine starts.

In the fuel-injection system for self-igniting internal combustion engines designed according to the invention, the low-pressure accumulator is filled before the start of the internal combustion engine via an overflow valve which is connected between the high-pressure pump of the fuel injection system and the low-pressure accumulator. In this way it is possible to fill the low-pressure accumulator even without an upstream low-pressure pre-feed pump.

A fuel injection system for self-igniting internal combustion engines provided with a high-pressure accumulator comprises a high-pressure part and a low-pressure part. In the high-pressure section, fuel is fed from a fuel tank to a high-pressure accumulator via a high-pressure pump and a high-pressure line. Injectors are connected to the high-pressure accumulator via high-pressure supply lines. The injectors are supplied with fuel from the high-pressure accumulator via the high-pressure supply lines.

To operate the injectors, it is necessary that the hydraulic coupler used to control the valve needle is subjected to a return counter pressure. This is achieved in that the injectors in the low-pressure section are connected to a low-pressure accumulator via injector return lines. A pressure-maintaining valve in the low-pressure accumulator is used for a pressure of <50 bar, preferably <20 bar and in particular <10 kept in cash. As soon as the pressure in the low-pressure accumulator exceeds the opening pressure of the drain-holding valve, the fuel is returned to the fuel tank via a return line. To build up the required drain in the low-pressure reservoir, the low-pressure reservoir is connected to the high-pressure line of the high-pressure part via an overflow valve and an overflow line.

To fill the low-pressure accumulator, the overflow valve is designed in such a way that the overflow valve is opened when the high-pressure part is relieved of pressure, thus establishing a connection from the high-pressure part to the low-pressure accumulator. The closing pressure of the overflow valve is dimensioned so that the overflow valve closes at a pressure in the range of 3 to 7 bar. The closing pressure of the overflow valve is thus below the opening pressure of the drain-holding valve.

The closing pressure of the overflow valve is generated in that a valve spring is provided in the overflow valve, the spring force of which corresponds to the pressure force which acts on the pressure surface of the valve piston. The valve piston is guided in a valve guide with little play. The fuel leakage flow through the low-clearance guide is collected in a low-pressure chamber delimited by the valve piston and returned to the fuel reservoir via a return.

drawing

The invention is described in more detail below with reference to a drawing. It shows:

It shows:

FIG. 1 shows a fuel injection system according to the prior art with an electrical low-pressure prefeed pump,

FIG. 2 shows a fuel injection system with overflow valve designed according to the invention,

Figure 3 shows an overflow valve designed according to the invention. Δ πcffi hrπn σcvnri -3ntι-> n

Figure 1 shows a fuel injection system according to the prior art with an electric low-pressure prefeed pump.

In a fuel injection system for supplying a self-igniting internal combustion engine, fuel is supplied from a fuel reservoir (not shown here) to a pre-feed pump 2 via a fuel feed line 1. In the pre-feed pump 2, the fuel is pre-compressed and further fed via a low-pressure line 3 to a high-pressure pump 4, in which the fuel is compressed onto the high-pressure storage tank and fed to a high-pressure tank 5. The pressure required to operate the internal combustion engine in the high-pressure accumulator 5 is in the range from 100 to 2000 bar. The fuel is supplied to the injectors 7 from the high-pressure accumulator 5 via high-pressure feed lines 6. In addition to the fuel injection system with six injectors shown in FIG. 1, to which an internal combustion engine with six cylinders is assigned, the fuel injection system can also comprise any other number of injectors.

The fuel required for the operation of the injectors 7, which is not injected into the combustion chamber of the internal combustion engine, is fed to a low-pressure accumulator 9 via injector return lines 8. The pressure in the low-pressure accumulator 9 is maintained in such a way that safe operation of the injectors is ensured. In particular when using piezo-controlled injectors, back pressure at the hydraulic coupler of the injector between 5 bar and 10 bar is required for safe operation over the entire speed range of the internal combustion engine.

A constant drain in the low-pressure accumulator 9 is achieved in that the low-pressure accumulator 9 is closed off by a pressure-maintaining valve 11. When the opening pressure of the pressure control valve 11 is exceeded, the pressure control valve 11 opens and fuel flows via a low pressure return to 13 back into the pressure control line 3. As soon as enough fuel has drained from the pressure control accumulator 9 that the opening pressure of the pressure control valve 11 falls below, the pressure control valve 11 closes again.

In order to keep the pressure in the high-pressure accumulator 5 constant when fuel is continuously being delivered by the high-pressure pump 4, the high-pressure accumulator 5 is closed off by a pressure regulating valve 10. As soon as the pressure in the high-pressure accumulator 5 exceeds the opening pressure of the drain control valve 10, the pressure control valve 10 opens and fuel runs via a return line 12 back into the fuel reservoir. Alternatively, systems with controllable fuel delivery through the high-pressure pump 4 are also known, in which the pressure control in the high-pressure accumulator 5 takes place by varying the pump delivery range and as a result of which a pressure control valve 10 can be dispensed with.

FIG. 2 shows a fuel injection system with an overflow valve designed according to the invention.

In contrast to FIG. 1, in the fuel injection system designed according to the invention, no prefeed pump 2 is connected between the fuel reservoir and the high-pressure pump 4. In the fuel injection system designed according to the invention, the fuel is conveyed directly from the fuel reservoir via the fuel feed line 1 and a high-pressure line 32 into the high-pressure accumulator 5 by means of the high-pressure pump 4. In such systems, a mechanically driven pre-feed pump 2 is usually integrated into the high-pressure pump 4, as a result of which the area after the pre-feed pump 2 is no longer accessible from the outside. The injectors 7 are fed with fuel from the high-pressure accumulator 5 via the high-pressure feed line 6. The fuel required for the hydraulic operation of the injectors 7, which is not injected into the combustion chambers of the internal combustion engine, is fed to the low-pressure accumulator 9 via the injector return lines 8. The low-pressure accumulator 9 is closed with the drain-holding valve 11. As soon as the drain in the low-pressure reservoir 9 exceeds the opening pressure of the drain-holding valve 11, the drain-holding valve 11 opens and fuel flows back into the fuel reservoir via the return line 12.

To fill the low-pressure accumulator before the internal combustion engine starts, an overflow line 33 branches off from the high-pressure line 32 behind the high-pressure pump 4. The overflow line 33 is connected to the low-pressure accumulator 9 via an overflow valve 15 and a low-pressure connection 34. The connection of the overflow valve 15 to the overflow line 33 can e.g. through a high-pressure connection 17 with a suitable union nut 19. The connection of the overflow valve 15 to the low-pressure connection 34 takes place via a low-pressure connection 25. Fuel which occurs as a result of the leakage flow is collected in a low-pressure chamber 28 and passed back into the fuel reservoir via a leakage line 35 which is connected to the return line 12. The leakage line 35 is attached to a return port 26 on the overflow valve 15. Since the line on the low-pressure side of the fuel injection system is usually designed as plastic hoses with an integrated fabric, the return connection 26 and the low-pressure connection 25 are designed as connection nipples for hoses.

The overflow valve 15 is designed so that it is open as long as the pressure in the high pressure region is lower than the closing pressure of the overflow valve 15. The closing pressure of the overflow valve 15 is selected such that it is somewhat lower than the drain in the low-pressure accumulator 9 delimited by the drain-holding valve 11 the open overflow valve 15 also fills the low-pressure accumulator 9. As soon as the closing pressure of the overflow valve 15 is reached, the overflow valve 15 is closed by the drain built up in the overflow line 33 by means of the high-pressure pump 4. As soon as the overflow valve 15 is closed, the drain in the high-pressure reservoir 5 is built up further until the necessary operating pressure is reached. Filling the low-pressure accumulator 9 via the overflow valve 15 ensures that a sufficiently high return counterpressure prevails at the injectors 7 when one of the injectors 7 is actuated for the first time, so that a hydraulic coupler, which is a piezo actuator for stroke translation, ie Stroke extension is assigned, can be filled reliably. The further pressure build-up in the low-pressure accumulator 9 until the operating pressure is reached is then achieved by switching off the fuel returning from the injectors 7.

FIG. 3 shows a detailed view of the overflow valve.

The overflow valve 15 comprises a valve housing 18, a valve piston 21 and a valve spring 24. A cover surface 22 and a seat surface 36 opposite the pressure surface 22 are formed on the valve piston 21. The seat surface 36 forms a valve seat 23 with the valve housing 18. In the position of the valve piston 21 shown in FIG. 3, the overflow valve 15 is open. The pressure surface 22 of the valve piston 21 points in the direction of a high-pressure connection 16. The high-pressure connection 16 comprises the high-pressure connection 17, which preferably closes off the overflow line 33. The high-pressure connection 17 is fastened to the valve housing 18 by means of the union nut 19. A spring force F is applied to the valve piston 21 by the valve spring 24. The spring force F is dimensioned such that the overflow valve 15 closes when a defined pressure in the high-pressure connection 16 is reached. The force acting on the cover surface 22 of the valve piston 21 can be according to

p • - • d2, p = drain in the return 4 d = diameter drain area 22

to calculate.

As soon as the force on the pressure surface 22 exceeds the spring force F of the valve spring 24, the overflow valve 15 closes; this is the case if E-4. - P> PschweU = - - T ^lrd - L d

The valve spring 24 used to open the valve is located on the valve piston 21 on a spring seat surface 29 and 30 on a spring chamber boundary wall on the valve housing 18 for accommodating the valve spring 24, a spring chamber ^'31 is accommodated in the valve housing 18th Furthermore, a bore in the valve housing 18 is preferably made centered on the spring chamber 31. The bore serves as a valve guide 27 and forms a low-pressure chamber 28 behind the valve piston 21. The diameter of the valve guide 27d is selected so that the valve piston 21 is guided with little play. To fill the low-pressure accumulator 9, fuel flows through the high-pressure connection 16 around the valve piston with the conical seat 36 into the spring chamber 31. From there, the fuel leaves the overflow valve 15 in the direction of the low-pressure accumulator 9 via the low-pressure connection 25 of the fuel flows along the valve guide 27 into the low-pressure chamber 28. The fuel that flows along the valve guide 27 serves at the same time to lubricate the valve piston 21 in the valve housing 18. Since the low-pressure chamber 28 is in direct connection with the fuel storage container, there is approximately the same the same pressure as in the fuel tank. Because of the difference in pressure between the spring chamber 31 and the low-pressure chamber 28, new fuel always flows into the low-pressure chamber 28. The fuel from the low-pressure chamber 28 is fed back into the fuel reservoir via the return connection 26.

In addition to the connection nipples for the low-pressure connection 25 and the return connection 26 shown in FIG. 3, the return connection and the low-pressure connection 25 can also take any other suitable form known to the person skilled in the art for connecting the low-pressure connection 34 or the leakage line 35. Furthermore, the overflow valve 15 can be connected to the overflow line 33 in addition to the screw connection shown with the high pressure connection 17 and the union nut 19 with any other detachable or non-detachable connection known to the person skilled in the art. The connections must in any case be stable against the drain generated by the high pressure pump 4. In addition to the screw connection shown, flange connections or welded connections are also possible. Furthermore, the low-pressure connection 25 or the return connection 26 can also be made as a flange connection, screw connection or, when using metallic pipelines, by welding. An adhesive connection is also conceivable for the connections which are not particularly stressed by a high pressure. also be designed as a ball seat, flat seat or slide, or any other form known to the person skilled in the art. Thus, each 2-way valve is suitable as an overflow valve 15, which closes the connection from the overflow line 13 into the low-pressure accumulator 9 at a predetermined closing pressure.

Reference list fuel supply line pre-feed pump low-pressure line high-pressure pump high-pressure accumulator high-pressure supply line injector injector return line low-pressure accumulator (return rail) drain control valve drain control valve return line

Niederdrackrücklauf

overflow

Hochdrackverbindung

Hochdrackanschluß

valve housing

Nut

pressure chamber

plunger

Drackfläche

valve seat

valve spring

Niederdrackanschluß

Return connection

Valve guide (low backlash)

Niederdrackraum

Spring bearing surfaces

Spring chamber boundary wall

spring chamber

Hochdrackleitung

overflow

Low pressure connection

leakage line

Seat cushion force in opening direction f. 21

Claims

r Pafp.n -. tnn <-. τ.-ri. —Ir- "hρ ~

1. Fuel injection system for internal combustion engines, comprising a high-pressure part and a low-pressure part, fuel being supplied from a fuel tank via a high-pressure pump (4) and a high-pressure line (32) to a high-pressure accumulator (5) in the high-pressure part, and injectors (7) via high-pressure supply lines (6 ) are supplied from the high-pressure accumulator (4) and the injectors (7) in the low-pressure section are connected to a low-pressure accumulator (9) via injector return lines (8), with a drain of <50 bar being held in the low-pressure accumulator (9) by a drain holding valve (11) and at a pressure in the low-pressure accumulator (9) above the opening pressure of the drain-holding valve (11), the fuel is returned to the fuel tank via a return line (12), characterized in that the low-pressure accumulator (9) via an overflow valve (15) and a Ü - Overflow line (33) connected to the high-pressure line (32) of the high-pressure part n is.

2. Fuel injection system according spoke 1, characterized in that the overflow valve (15) is open when the high-pressure part is relieved of pressure.

3. Fuel injection system according to claim 1, characterized in that the overflow valve (15) is closed when a closing pressure which is below the opening pressure of the pressure-maintaining valve (11) is reached by the action of the fuel compressed by means of the high-pressure pump (4).

4. Fuel injection system according to one or more of claims 1 to 3, characterized in that the overflow valve (15) contains a valve spring (24) whose spring force F corresponds to the force applied by the closing pressure on the overflow valve (13).

5. Fuel injection system according to one or more of claims 1 to 4, characterized in that the overflow valve (15) contains a low-pressure chamber (28) which is connected to the return line (12) via a leakage line (35).

6. Fuel injection system according to one or more of claims 1 to 5, characterized in that the injectors (7) are piezo-controlled.

7. Fuel injection system according to one or more of claims 1 to 6, characterized in that the drain in the low-pressure accumulator (9) is <10 bar.