EP1125045B1 - Fuel injection system for an internal combustion engine - Google Patents

Abstract

A fuel injection system having at least two different, high system pressures for an internal combustion engine, includes a first central pressure reservoir for the lower system pressure and includes a second central pressure reservoir, supplied from a high-pressure pump, for the higher system pressure, both pressure reservoirs being connectable by line to the injector of each cylinder, and to increase the efficiency, a two-stage high-pressure pump, by whose lower stage the first pressure reservoir and by whose higher stage the second pressure reservoir are supplied.

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 a fuel injection system is, for example through EP 0 711 914 A1.

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 releases the injection opening for an injection of the fuel. The pressure at which fuel emerges from the nozzle chamber into the cylinder is referred to as the injection pressure , while a system pressure is understood to mean the pressure under which fuel is available or is stored in the injection system. A stroke-controlled 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. In the case of a combined fuel metering , there is a switch between different injection pressures and only one common valve for metering the fuel is used, this switchover being able to take place either centrally, ie before the fuel is distributed to the individual cylinders, or locally, ie for each cylinder individually.

In the pressure-controlled known from EP 0 711 914 A1 The injection system is fueled using a high pressure pump to a first high system pressure of around 1200 bar compressed and stored in a first pressure accumulator. Furthermore, the fuel is under high pressure also promoted in a second pressure accumulator, in which by regulating its Fuel supply by means of a 2/2-way valve a second high system pressure of approx. 400 cash is maintained. Via a valve control unit, either the lower one or higher system pressure is directed into the nozzle area of an injector. There is through the pressure a spring-loaded valve body is lifted off its valve seat, allowing fuel to flow out the nozzle opening can escape.

A disadvantage of this known injection system is that initially all of the fuel must first be compressed to the higher system pressure level, then a part of the fuel back to the lower system pressure level.

Furthermore, a stroke-controlled injection system is known from WO 98 09068 A. the fuel from a fuel tank to two different high system pressures each compressed by a pump and conveyed to a pressure accumulator. A valve control can either use the higher or lower system pressure for a Injection can be directed into the nozzle space of an injector.

Advantages of the invention

The fuel injection system according to the invention, which is pressure-controlled or stroke-controlled can be, has the characteristic features of the to increase the efficiency Claim 1 on.

According to the invention, it is proposed to use only the fuel for one pressure accumulator compress the higher system pressure level while fueling the other Pressure accumulator is only compressed to the lower system pressure level.

The lower amount of fuel according to the invention leads to the higher system pressure in addition to a higher degree of efficiency and less stress on the Pump components and, since the higher system pressure is not opposite Normal pressure, but only compared to the other high, however Sealing deeper system pressure is a better one Sealing and therefore less leakage.

Further advantages and advantageous configurations of the object the invention are the description, the drawing and removable from the claims.

drawing

Fig. 1a

ein hubgesteuertes Kraftstoffeinspritzsystem mit einer zweistufigen Hochdruckpumpe für zwei Druckspeicher und mit einer kombinierten Kraftstoffzumessung im Injektor;

Fig. 1b

ein hubgesteuertes Kraftstoffeinspritzsystem mit einer zweistufigen Hochdruckpumpe für zwei Druckspeicher und mit einer kombinierten Kraftstoffzumessung außerhalb des Injektors;

Fig. 2a

ein druckgesteuertes Kraftstoffeinspritzsystem mit einer zweistufigen Hochdruckpumpe für zwei Druckspeicher und mit einer kombinierten Kraftstoffzumessung im Injektor;

Fig. 2b

ein druckgesteuertes Kraftstoffeinspritzsystem mit einer zweistufigen Hochdruckpumpe für zwei Druckspeicher und mit einer kombinierten Kraftstoffzumessung außerhalb des Injektors;

Fig. 3

ein druckgesteuertes Kraftstoffeinspritzsystem mit einer zweistufigen Hochdruckpumpe für zwei Druckspeicher und mit einer kombinierten zentralen Kraftstoffzumessung; und

Fig. 4

ein nicht erfindungsgemäß druckgesteuertes Kraftstoffeinspritzsystem mit zwei jeweils von einer Hochdruckpumpe gespeisten Druckspeichern und mit einer kombinierten zentralen Kraftstoffzumessung.

Embodiments of the fuel injection system according to the invention are shown schematically in the drawing and explained in the following description. Show it:

Fig. 1a

a stroke-controlled fuel injection system with a two-stage high-pressure pump for two pressure accumulators and with a combined fuel metering in the injector;

Fig. 1b

a stroke-controlled fuel injection system with a two-stage high-pressure pump for two pressure accumulators and with a combined fuel metering outside the injector;

Fig. 2a

a pressure-controlled fuel injection system with a two-stage high-pressure pump for two pressure accumulators and with a combined fuel metering in the injector;

Fig. 2b

a pressure-controlled fuel injection system with a two-stage high-pressure pump for two pressure accumulators and with a combined fuel metering outside the injector;

Fig. 3

a pressure-controlled fuel injection system with a two-stage high-pressure pump for two pressure accumulators and with a combined central fuel metering; and

Fig. 4

a fuel injection system not pressure-controlled according to the invention with two pressure accumulators each fed by a high-pressure pump and with a combined central fuel metering.

Description of the embodiments

In the embodiment of a stroke-controlled fuel injection system 1 shown in Fig. 1a , a quantity-controlled two-stage high-pressure pump 2 delivers fuel 3 from a storage tank 4 at high pressure via a delivery line 5 into a central pressure accumulator 6 (high-pressure common rail), of which several, the number individual cylinders discharge corresponding high-pressure lines 7 to the individual injectors 8 (injection device) projecting into the combustion chamber of the internal combustion engine to be supplied. Only one of the injectors 8 is shown in FIG. 1a. A system pressure of approximately 300 bar to 1800 bar can be stored in this pressure accumulator 6. Another central pressure accumulator (low-pressure common rail) 9 is used to inject fuel with a lower system pressure for pre-injection and post-injection (HC enrichment for exhaust gas aftertreatment and soot reduction) as well as for displaying an injection process with a plateau (boat injection) discharge to the injectors 8 analogously to the high-pressure lines 10 . In the first stage of the high-pressure pump 2, the fuel is compressed to this lower system pressure of, for example, 300 bar and stored in the pressure accumulator 9. In the second stage of the high-pressure pump 2, the pressure generation is regulated to the higher system pressure up to approximately 1800 bar and stored in the pressure accumulator 6.

The injection takes place via a combined local fuel metering with the help of the injectors 8. The injector 8 has a piston-shaped valve member 11 which is axially displaceable in a guide bore and has a conical valve sealing surface 12 at one end, with which it has a valve seat surface on the injector housing of the injector 8 interacts. Injection openings 13 are provided on the valve seat surface of the injector housing. A nozzle chamber 14 and a control chamber 15 are formed within the guide bore. The nozzle chamber 14 arises due to a reduction in the cross section of the valve member 11. The nozzle chamber 14 and the control chamber 15 are continuously connected to one of the two pressure accumulators 6, 9 via pressure lines 16 and 17 and a 3/2-way valve 18 . The nozzle chamber 14 continues through an annular gap between the valve member 11 and the guide bore up to the valve seat surface of the injector housing.

In a spring chamber 19, the end face 23 remote from its valve sealing surface 12 engages coaxially with a valve spring 20 also on the valve member 11, a pressure piece 22 to the control chamber 15 is limited. The spring chamber 19 is connected to the storage tank 4 via a leakage line 21 for fuel return. The control chamber 15 has an inlet with a first throttle 28 and an outlet to a pressure relief line 25 with a second throttle 24 , which is controlled by a 2/2-way valve 26 , from the fuel pressure connection. The nozzle chamber 14 continues through an annular gap between the valve member 11 and the guide bore up to the valve seat surface of the injector housing. The pressure piece 22 is pressurized in the closing direction by the pressure in the control chamber 15.

The 2/2 and 3/2 way valves 18, 26 are made by electromagnets to open or close or to switch the Fuel lines 7 and 10 actuated. The electromagnets are controlled by a control device that different Operating parameters (engine speed, ...) of the supply Monitor and process the internal combustion engine. The respective pressure in the two pressure reservoirs 6, 9 can detected by means of pressure sensors and by means of a control device be kept constant.

When the 2/2-way valve 26 is actuated (opened), the pressure in the control chamber 15 can be reduced, so that the pressure in the nozzle chamber 14 acting in the opening direction exceeds the pressure acting on the valve member 11 in the closing direction , The valve sealing surface 12 lifts off the valve seat surface and fuel is injected. The relief process of the control chamber 15 and thus the stroke control of the valve member 11 can be influenced by the dimensioning of the throttle 24 and a further throttle 28 . The end of the injection process is initiated by renewed actuation (closing) of the 2/2-way valve 26, which connects the control chamber 15 to the pressure line 17 again, so that a pressure builds up in the control chamber 15 again, the valve member 11 in the closing direction can move.

The 3/2-way valve 18 can also be a 2/2-way valve and a check valve to be replaced. Generally can instead of solenoid operated valves Piezo actuators are also used, which are necessary Temperature compensation and a possible force or have path translation. Instead of two separate ones Pressure accumulator for the two system pressures can also be used combined pressure accumulator (combined rail) provided his. An outer pressure storage space encloses the lower system pressure an internal pressure storage space with the higher system pressure. In this way, minor occur Pressure gradients on a housing of the pressure storage spaces exposure to lower material loads and, for example the formation of an even higher pressure in the Allow high pressure storage space.

In contrast to the exemplary embodiment in FIG. 1 a, the 3/2-way valve 18 in the fuel injection system shown in FIG. 1 b is not arranged in the injector but instead outside the injector 8 a, for example in the region of the pressure accumulators 6, 9. A smaller size of the injector 8a and an increased injection pressure can be achieved by utilizing wave reflections in the now longer pressure lines 16.

In the pressure-controlled injection system shown in FIG. 2 a, fuel is conveyed from a fuel tank 31 to the injectors 32 of four cylinders and from there via injection openings 33 into the combustion chamber 34 of the respective cylinder. A quantity-controlled two-stage high-pressure pump 35 is used to generate two different, high system pressures. In the first, lower pump stage, the fuel is compressed to a first high system pressure of approximately 300 bar, which is stored in a first pressure accumulator 36 (first rail). With the second, higher pump stage, the fuel is compressed to a second, higher system pressure of approximately 300 bar to approximately 1800 bar and then stored in a second pressure accumulator 37 (second rail). A control circuit with a pressure sensor is provided for each of the two pressure accumulators 36, 37. The lower system pressure level can be used for the pre-injection and, if necessary, for the post-injection as well as for the main injection if a low injection pressure is required.

To switch between the lower and the higher system pressure (combined pressure metering), a 2/2-way valve 38 for the high pressure side is provided as the switching element for each cylinder or injector 32, the output of which from the low pressure side is provided by a check valve 39 (or by a third / 2-way valve) is disconnected. Via a 3/2-way valve 40 , the respectively prevailing pressure is then conducted via a line 41 into the nozzle chamber 42 of the injector 2, which is designed in a pressure-controlled manner. That is, its nozzle needle 43 , which seals the injection openings 33, is opened by the pressure prevailing in the nozzle chamber 32 against the action of a closing force. In the exemplary embodiment shown, an injection with a lower injection pressure takes place by energizing the 3/2-way valve 10. By energizing the 2/2-way valve 38, a switch is then made for an injection with a high injection pressure, the check valve 39 causing an undesired return from the high pressure side to the Low pressure side prevented. At the end of the injection, the 3/2-way valve 40 is switched to leakage 44 . This relieves on the one hand the line 41 and on the other hand the nozzle space 42, so that the spring-loaded nozzle needle 43 closes the injection openings 33 again.

While the valve arrangement formed from the two valves 38, 40 and the check valve 39 is located in the injector 32 in the exemplary embodiment in FIG. 2a, in the injection system shown in FIG. 2b this valve arrangement is outside the injector 32a , for example in the region of the pressure accumulator 36. 37 arranged. In this way, a smaller size of the injector 32a and an increased injection pressure can be achieved by utilizing wave reflections in the now longer injection line.

In the injection system shown in FIG. 3 , it is possible to switch between the two system pressure levels centrally via a first 3/2-way valve 45 (or via a 2/2-way valve and a check valve) and then the respective pressure centrally via a second 3/2 -Way valve 46 are directed to a central distributor device 47 , which distributes the fuel via lines 48 to the injectors 32 of the individual cylinders for injection. In this exemplary embodiment, injection with the lower system pressure takes place by energizing both 3/2-way valves 45, 46, and injection with the higher system pressure by energizing only the second 3/2-way valve 46. At the end of the injection, the second 3/2 -Way valve 46 switched to leakage 49 and thus the respective line 48 is relieved via a valve arrangement comprising a check valve 50 and a throttle 51 provided between the distributor device 47 and the injector 32.

In the example of FIG. 4 which is not according to the invention, the two-stage high-pressure pump 35 shown in FIG. 2 is replaced by a high-pressure pump 35a which only feeds the first pressure accumulator 37 and a high-pressure pump 35b which only feeds the second pressure accumulator 36.

Both magnetic actuators and piezo actuators, which enable faster switching of the valves, be used. The 3/2-way valves can also each with a combination of two 2/2-way valves be replaced. For switching the two system pressure levels is also an arrangement of 2/2-way valve and check valve possible with a given relief of the injector.

Claims (3)

1. Fuel injection system (1; 30) having at least two different, high system pressures for an internal combustion engine, having a first, central pressure accumulator (9; 36) for the lower system pressure and having a second, central pressure accumulator (6; 37), fed by a high-pressure pump, for the higher system pressure, both pressure accumulators (6, 9; 36, 37) being connected by lines to the injector (8; 8a; 32) of each cylinder, characterized in that a two-stage high-pressure pump (2; 35) is provided, by whose lower stage the first pressure accumulator (9; 36) is fed, and by whose higher stage the second pressure accumulator (6; 37) is fed.
2. Fuel injection system according to Claim 1, characterized in that the injector (8; 8a) is stroke-controlled.
3. Fuel injection system according to Claim 1, characterized in that the injector (32) is pressure-controlled.

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