DEVICE FOR METERING FUEL INTO THE EXHAUST SYSTEM OF AN INTERNAL COMBUSTION ENGINE

Abstract

Proposed is a device for metering fuel into the exhaust system of an internal combustion engine. An injection valve is arranged in the exhaust system and is cooled by a flowing cooling liquid even in its closed state. The injection valve is supplied with fuel via a fuel inflow, from which a first partial flow is injected into the exhaust gas and from which a second partial flow is recirculated via a fuel collecting return line into a fuel storage tank. The fuel inflow is fed from a low-pressure system of an injection system which serves for metering fuel for combustions which take place in a combustion chamber of the internal combustion engine. The device has a damping mechanism, which is hydraulically connected to the fuel inflow, for damping pressure oscillations.

Description

PRIOR ART

The present invention relates to a device for metering fuel to the exhaust system of an internal combustion engine, having an injection valve disposed in the exhaust system, which valve, even in the closed state, is cooled by a flowing cooling fluid and is supplied via a fuel inlet with fuel, of which a first partial flow is injected into the exhaust gas and a second partial flow is returned to a fuel tank via a fuel collecting return line.

One such device is known from German Patent Disclosure DE 103 24 482 A1. The injection of the fuel into the exhaust system is done with the goal either of varying the exhaust gas temperature, or to trip and maintain chemical reactions in the exhaust system that serve to regenerate an exhaust gas posttreatment component when liquid fuel is injected into the comparatively hot exhaust gas, the fuel evaporates and extracts heat from the exhaust gas, so that under some circumstances, this provision can be employed to protect components such as exhaust pipe elbows and/or exhaust gas turbochargers from overheating. The certain circumstances include in particular a stoichiometric or reducing exhaust gas atmosphere. If conversely the injection takes place in an oxidizing exhaust gas atmosphere, then chemical reactions can be tripped. For instance, chemical reactions that proceed exothermically can be tripped for heating such exhaust gas posttreatment components as particle filters and/or catalytic converters. Alternatively or in addition, by the injection of fuel into the initially oxidizing exhaust gas atmosphere, a reducing exhaust gas atmosphere is generated, which serves to regenerate an exhaust gas posttreatment component. For instance, nitrogen oxide storage catalytic converters that are extensively laden with nitrogen oxide compounds are regenerated in a reducing exhaust gas atmosphere at an elevated exhaust gas temperature. The stored nitrogen compounds break down in the process, and the resultant molecular nitrogen is removed from the storage catalytic converter along with the exhaust gas.

In German Patent Disclosure DE 103 24 482 A1, the injection of fuel is mentioned in conjunction with the regeneration of a particle filter. In this case, the fuel is injected into an oxidizing exhaust gas atmosphere, which with an oxidation catalytic converter leads to exothermic reactions. As a result, the temperature of the still-oxidizing exhaust gas atmosphere is increased so much that an ignition temperature for the soot deposited in the particle filter is exceeded, and the soot particles combust in the oxidizing exhaust gas atmosphere. The injection valve used in the subject of DE 103 24 482 A1 is triggered by a control unit with an electrical signal, so that the metering and the stream preparation are effected by a single valve. The delivery of fuel to the injection valve is effected via an electric pump, is controlled by a control unit in such a way that it pumps fuel to suit the demand to the injection valve disposed in the exhaust system.

The fuel pumped by the pump is carried through cooling conduits inside the injection valve before being split into a first partial flow to be injected and a second partial flow to be returned to a fuel tank via a fuel return line. For the control to suit demand of the pump, it is a prerequisite that this pump, its drive, and its triggering be designed quite especially for supplying the injection valve disposed in the exhaust system with fuel and is thus in particular not identical to the low-pressure pump of the injection system, with which fuel is pumped to a high-pressure pump that generates the injection pressure for combustions that take place in combustion chambers of the engine.

DISCLOSURE OF THE INVENTION

The present invention is distinguished over this prior art in that the fuel inlet is supplied from a low-pressure system of an injection system, serves to meter fuel for combustions that take place in a combustion chamber of the engine, and that the device has a damping device, communicating hydraulically with the fuel inlet, for damping pressure fluctuations.

By supplying the device for metering fuel to the exhaust system from the low-pressure system of the conventional injection system, a separate pump with its drive and its triggering can be dispensed with, which is advantageous in view of the costs of the exhaust gas posttreatment system as well as in view of the reliability of the system.

The supply from the low-pressure system of the conventional injection system can, however, lead to the feeding of pressure fluctuations from the low-pressure system into the device. The amplitude of such pressure fluctuations may be a multiple of the mean pressure in the low-pressure system. Such pressure fluctuations can impair the metering of fuel into the exhaust system, since they can adversely affect the opening performance of the injection valve. Hence in pressure-controlled injection valves, a so-called buzzing mode is the goal, in which the injection valve opens and closes in rapid succession, also known as buzzing.

In the process, the injection valve is opened counter to the force of a spring by the pressure in the fuel system. The opening of the injection valve causes the pressure upstream of the injection valve to quickly break down, leading to closure of the injection valve. With the injection valve closed, the pressure upstream of the injection valve builds up again, so that it re-opens. As a result, the injection valve opens and closes in the rapid succession also known as buzzing. As a result of the buzzing, the injection stream is interrupted again and again, which reduces droplet size of the injected fuel and thus contributes to good preparation of the fuel for evaporation in the exhaust gas. The desired buzzing occurs only within a comparatively narrow pressure range, which is departed from when the aforementioned pressure fluctuations occur.

The damping device communicating hydraulically with the fuel inlet damps pressure fluctuations that have been fed in and thus assures that the buzzing mode needed for the stream preparation is maintained. Alternatively to stream preparation by buzzing on the part of the injection valve, an injection valve with an injection port plate can be used for stream preparation. One such injection valve is known for instance from International Patent Disclosure WO 94/00686. In this type of injection valves as well, the quality of the stream preparation depends on the injection pressure, so that damping pressure fluctuations that have been fed in is an advantage in this type of injection valves as well.

Further advantages will become apparent from the dependent claims, the description, and the accompanying drawings.

It is understood that the characteristics mentioned above and to be described below can be employed not only in the specifically recited combination but in other combinations as well or on their own, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in the drawings and will be described in further detail in the ensuing description. The same reference numerals in different drawings each designate the same elements. The drawings, each in schematic form, show the following:

FIG. 1, a first exemplary embodiment of the invention;

FIG. 2, a second exemplary embodiment of the invention;

FIG. 3, a third exemplary embodiment of the invention; and

FIG. 4, a fourth exemplary embodiment of the invention.

EMBODIMENT(S) OF THE INVENTION

In detail, FIG. 1 shows a device 10 for metering fuel to the exhaust system 12 of an internal combustion engine. The device 10 has an injection valve 14, which is disposed in the exhaust system 12. The term disposition in the exhaust system 12 will be understood to mean a disposition in which the injection valve 14 is mounted at an opening of an exhaust-gas-carrying line in such a way that it protrudes into the line and tightly closes the opening. The device 10 has a fuel inlet 16, by way of which the device 10 is supplied with fuel. The fuel inlet 16 is supplied from a low-pressure system 18 of an injection system, which serves to meter fuel for combustions that take place in a combustion chamber of an internal combustion engine.

Embodiments of such injection systems include a low-pressure circuit and a high-pressure circuit. In the low-pressure circuit, a low-pressure pump generates a fuel pressure on the order of magnitude of 2 to 5 bar, which is increased by a high-pressure pump or individual unit fuel injectors to an injection pressure on the order of magnitude of between 1000 and 2000 bar. The device 10 furthermore has a damping device 20, hydraulically with the fuel inlet 16, for damping pressure fluctuations and/or pressure waves.

The injection valve 14 used in the embodiment of FIG. 1 is a pressure-controlled injection valve 14, which is connected via an electrically controllable metering valve 22 to a calming volume 24 of the damping device 20. The term pressure-controlled injection valve 14 will be understood to mean an injection valve in which a rising fuel pressure inside a pressure chamber of the injection valve 14 lifts a sealing body, such as a nozzle needle, from its sealing seat counter to the force of a restoring spring and in so doing uncovers an injection cross section.

In the embodiment of FIG. 1, the pressure in the pressure chamber of the injection valve 14 is controlled by triggering of the metering valve 22 by a control unit 26. As a result, the fuel flow from the damping volume 24 to the injection valve 14 is controlled. The triggering is preferably effected such that the metering valve 22 is largely closed whenever no injection is to take place. Then no fuel pressure can build up in the pressure chamber of the injection valve 14. Any fuel pressure that may still remain diminishes by way of the first return line 30 provided with a return throttle restriction 28, so that the injection valve 14 closes and/or remains closed. This embodiment therefore employs two valves 14, 22 for metering the fuel to the exhaust gas; the control of the injection quantity is done with the metering valve 22, and the stream or spray preparation is done with the pressure-controlled injection valve 14.

A first partial flow j_e of the fuel diverted into the device 10 from the low-pressure system 18 is injected into the exhaust gas in the exhaust system 12. A second partial flow j_r of the inflowing fuel flows back into a fuel tank via a fuel collecting return line 32. In the open state, the injection valve 14 is cooled by the fuel quantity injected with the first partial flow j_e into the exhaust gas. Moreover, in the closed state as well, the injection valve 14 is cooled by a flowing cooling fluid. In the embodiment of FIG. 1, fuel is continuously supplied to the injection valve 14, from which fuel a partial flow j_r1 flows through the injection valve 14 and is carried away again via the first return line 30. The partial flow j_r1 absorbs heat from the injection valve 14, transports it away via the first return line 30, and in this way represents an embodiment of a cooling fluid stream which comprises fuel as the cooling medium. In one embodiment, the return line 30 discharges into the fuel collecting return line 32.

The absorption of heat takes place in one embodiment in such a way that the partial flow j_r1 is also carried through the pressure chamber of the injection valve 14 before it is received by the first return line 30. When the injection valve 14 is closed, the flow is controlled by a clocked opening and closure of the metering valve 22, which is done such that the pressure in the pressure chamber does not exceed the opening pressure of the injection valve 14. In the event that the injection valve 14 is to be opened, the flow is increased by the metering valve 22, so that by way of the return throttle restriction 28 in the first return line 30, a pressure can build up that exceeds the opening pressure of the injection valve 14.

In the embodiment of FIG. 1, the damping device 20 has the damping volume 24, which is disposed in the fuel inlet 16 spatially separately from the injection valve 14. The damping volume 24 damps the amplitude of pressure fluctuations that are fed from the low-pressure system 18 into the device 10. An inlet throttle restriction 34 that is optionally present provides for additional damping and pressure decoupling between the low-pressure system 18 and the device 10. As an additional advantage, the inlet throttle restriction 34 provides a reduced feedback of events in the device 10 on the pressure level in the low-pressure system 18.

The damping volume 24 is connected to the fuel collecting return line 32 via the pressure control valve 36. The pressure control valve 36 is preferably a pressure-controlled valve, which opens automatically at an adjustable opening pressure and closes again automatically when the pressure drops below the opening pressure. In this way, pressure peaks in the damping volume 24 can be diminished by opening the pressure-controlled pressure control valve 36, minimizes the influence of such pressure peaks on the opening and closing of the injection valve 14.

The aforementioned pressure peaks occur in the low-pressure system 18 for instance as a consequence of pressure generation with a gear pump, in which the individual pumping teeth each lead to corresponding pressure peaks. A further cause of pressure peaks is feedback from the high-pressure circuit, which serves to supply the combustion chambers of the engine with fuel, on the low-pressure system. In injection systems for diesel engines, the pressure peaks may for instance attain values on the order of magnitude of 20 bar, and the mean pressure level in the low-pressure system 18 is on the order of magnitude of 2 to 5 bar.

The embodiment of FIG. 1 furthermore shows a blocking valve 38, which is disposed upstream of the injection valve 14 and which in the closed state interrupts the supply of fuel to the injection valve 14. This blocking valve 38 has the task of suppressing fuel delivery to the exhaust system 12 in certain situations, such as an accident, so that an uncontrolled outflow of fuel into the exhaust system 12 will not occur. For that purpose, the blocking valve 38 is preferably embodied as an electrically controllable valve. Such a blocking valve 38 may be disposed both upstream of the damping volume 24 and downstream of the damping volume 24.

In a preferred embodiment, the injection valve 14 is arranged, a suitable injection pressure, to operate in a buzzing mode and thereby to assure good spray preparation or stream preparation. To that end, the opening pressures, in particular, of the injection valve 14 and control valve 36 are adapted to one another.

The embodiment in FIG. 2 also shows a device 40 for metering fuel to the exhaust system 12 of an internal combustion engine, with an injection valve 42 which is disposed in the exhaust system 12 and even in the closed state is cooled by a flowing cooling fluid, and with a fuel inlet, by way of which the device 40 is supplied with a first partial flow j_e, which is injected into the exhaust gas, and a second partial flow j_r, which returns to a fuel tank via a fuel collecting return line 32.

Here as well, the fuel inlet 16 is supplied from the low-pressure system 18 described of an injection system of the engine. The damping device 20 communicating hydraulically with the fuel inlet 16 has a damping volume 44, which is connected to the fuel collecting return line 32 via the pressure control valve 36. In a departure from the subject of FIG. 1, the damping volume 44 in FIG. 2 is designed as a cooling reservoir 44, and the injection valve 42 is disposed at least partly inside the cooling reservoir 44. Fuel flows through the cooling reservoir 44, and pressure fluctuations occurring in the fuel inlet 16 are damped by the damping volume of the cooling 44 and the action of the pressure control valve 36 before they have an effect on the metering of fuel to the exhaust gas.

Within the scope of the preferred embodiment, the injection valve 42 is embodied as an electrically controlled injection valve 42, which is arranged for injecting a quantity of fuel to be injected as a function of an electrical trigger signal of the control unit 26. In a departure from the subject of FIG. 1, in the subject of FIG. 2 a single valve 42 is therefore used for both the metering and spray preparation or stream preparation. In comparison to the embodiment of FIG. 1, in which the metering and spray or stream preparation are spatially separated by two valves 22, in the embodiment of FIG. 2 there is reduced effort and expense for integration and application. This advantage is due to the fact that the metering and stream or spray preparation with two valves 22, 14 lead to a hydraulically highly complex performance of the system, with a correspondingly high amount of effort and expense for integration and application. In such a system with two valves 22, 14, the dynamic performance, especially the dynamic performance of the injection valve 14, moreover makes precise diagnosis of leaks, especially leaks between the metering valve 22 and the injection valve 14, more difficult.

In an embodiment, there is also a pressure sensor 48, detects the fuel pressure upstream of the injection valve 42 and forwards it to the control unit 26, which also controls the injection valve 42. The knowledge of the fuel pressure enables the control unit 26 to meter the flow quantity, which is dependent on the fuel pressure, through the injection valve 42, still more precisely.

The embodiment in FIG. 3 shows a device 50 in which once again fuel is metered to the exhaust system 12 of an internal combustion engine with an injection valve 42 disposed in the exhaust system, which injection valve is cooled even in the closed state by a flowing cooling fluid. In the embodiment of FIG. 3, the cooling is effected in the manner described in conjunction with FIG. 1. The subjects of FIGS. 1 and 3 differ from one another in that the combination of the electrically controllable metering valve 22 with the pressure-controlled injection valve 14 of FIG. 1 is replaced in the subject of FIG. 3 by an electrically controlled injection valve 42. The electrically controlled or controllable injection valve 42 is arranged for injecting a quantity of fuel to be injected as a function of an electrical trigger signal of the control unit 26. As in the subject of FIG. 2, thus in the subject of FIG. 3 as well a single valve 42 is used for both the metering and the spray preparation or stream preparation.

In addition, the device in FIG. 3 is also supplied via a fuel inlet 16 with fuel, of which a first partial flow j_e is injected into the exhaust gas and a second partial flow j_r is returned to a fuel tank via a fuel collecting return line 32. The fuel inlet 16 is supplied from the low-pressure system 18 of the injection system, which serves to meter fuel for combustion that takes place in a combustion chamber of the engine. The device 50 has a damping device 20, communicating hydraulically with the fuel inlet 16, that has a damping volume 24 which is connected to the fuel collecting return line 32 via a pressure control valve 36 and is disposed in the fuel inlet 16, spatially separately from the injection valve 42.

The embodiment of FIG. 4 represents a modification of the subject of FIG. 2. To that extent, FIG. 4 as well first shows a device 60 for metering fuel to the exhaust system 12 of an internal combustion engine, an injection valve 42, which is disposed in the exhaust system 12 and which in the closed state as well is cooled by a flowing cooling fluid and which is supplied with fuel via a fuel inlet 16. A first partial flow j_e of the fuel fed into the device 60 via the fuel inlet 16 is injected into the exhaust gas, and a second partial flow j_r is returned to a fuel tank via a fuel collecting return line 32. The fuel inlet 16 is supplied from the low-pressure system 18 of an injection system which serves to meter fuel for combustions that take place in a combustion chamber of the engine.

The device 60 has a damping device 20, communicating hydraulically with the fuel inlet 16, that has a damping volume 24 which is connected to the fuel collecting return line 32 via a pressure control valve 36 and is disposed in the fuel inlet 16, spatially separately from the injection valve 42. The injection valve 42 is an electrically controlled injection valve 42, which is arranged for injecting a quantity of fuel to be injected as a function of an electrical trigger signal of a control unit 26. Once again, a single valve 42 is used for both metering and the spray or stream preparation, so that once again the corresponding advantages that have already been explained in conjunction with FIG. 2 are obtained. The injection valve 42 is disposed at least partly in a cooling jacket 62 through which cooling medium flows. In a distinction from the embodiment of FIG. 2, however, it is not fuel but the cooling fluid of the engine that is used as the cooling medium. The lines 64, 66 serve to connect the cooling jacket 62 to a cooling system of the engine.

Claims

1-10. (canceled)

11. A device for metering fuel to an exhaust system (12) of an internal combustion engine, having an injection valve, which is disposed in the exhaust system and which even in a closed state of the injection valve, is cooled by a flowing cooling fluid, the injection valve being supplied via a fuel inlet with fuel, of which a first partial flow is injected into the exhaust gas and a second partial flow is returned to a fuel tank via a fuel collecting return line, the fuel inlet being supplied a low-pressure system of an injection system, which serves to meter fuel for combustions that take place in a combustion chamber of the engine, wherein the device has a damping mechanism which damps pressure fluctuations, and which communicates hydraulically with the fuel inlet.

12. The device as defined by claim 11, wherein the damping mechanism has a damping volume.

13. The device as defined by claim 12, wherein the damping volume is connected to the fuel collecting return line via a pressure control valve.

14. The device as defined by claim 12, wherein the damping volume is designed as a cooling reservoir, and the injection valve disposed at least partly inside the cooling reservoir.

15. The device as defined by claim 13, wherein the damping volume is designed as a cooling reservoir, and the injection valve disposed at least partly inside the cooling reservoir.

16. The device as defined by claim 14, wherein the injection valve is an electrically controlled injection valve, which is arranged for injecting a quantity of fuel as a function of an electrical trigger signal.

17. The device as defined by claim 15, wherein the injection valve is an electrically controlled injection valve, which is arranged for injecting a quantity of fuel as a function of an electrical trigger signal.

18. The device as defined by claim 12, wherein the damping volume is disposed in the fuel inlet separately from the injection valve.

19. The device as defined by claim 18 wherein the device has a pressure-controlled injection valve, which is connected to the damping volume via an electrically controllable metering valve.

20. The device as defined by claim 18, wherein the injection valve is an electrically controlled injection valve, which is arranged for injecting a quantity of fuel as a function of an electrical trigger signal.

21. The device as defined by claim 20, wherein the injection valve is disposed at least partly in a cooling jacket which a cooling medium flows.

22. The device as defined by claim 21, wherein that the cooling jacket is connected to a cooling system of the engine via lines.