CN106968844B

CN106968844B - Method for removing deposits or coverings from an exhaust gas feedback system

Info

Publication number: CN106968844B
Application number: CN201611053341.0A
Authority: CN
Inventors: C.旺德林; R.埃克; T.库恩; T.霍尔曼; U.舒尔茨
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2015-11-26
Filing date: 2016-11-25
Publication date: 2021-12-28
Anticipated expiration: 2036-11-25
Also published as: DE102016214284A1; CN106968844A

Abstract

The invention relates to an exhaust gas feedback system (4) for an internal combustion engine (1). The exhaust gas feedback system has at least one fuel injection valve (43), the spray cone of which is directed toward the exhaust gas feedback line (41) thereof. Fuel is injected into an exhaust gas feedback line (41) of an exhaust gas feedback system (4) of the internal combustion engine (1), so that deposits or coatings can be removed from the exhaust gas feedback system (4). The invention also relates to two methods for operating an internal combustion engine (1) having an exhaust gas feedback system (41). In this case, at least a portion of the fuel quantity intended for injection into an intake manifold injector (24 a, 24b, 24c, 24 d) in the internal combustion engine (1) is injected by means of a fuel injection valve (43) if the temperature of the inlet channel (22) of the internal combustion engine (1) falls below a predeterminable temperature threshold or if the ethanol concentration of the fuel to be injected exceeds a predeterminable ethanol threshold.

Description

Method for removing deposits or coverings from an exhaust gas feedback system

Technical Field

The present invention relates to an exhaust gas feedback system for an internal combustion engine. The invention also relates to two methods for operating an internal combustion engine having an exhaust gas feedback system, and to a method for removing deposits or coverings from an exhaust gas feedback system of an internal combustion engine. Furthermore, the invention relates to a computer program for carrying out each step of one of the methods according to the invention, and to a machine-readable storage medium on which the computer program is stored. Finally, the invention relates to an electronic control unit which is designed to carry out at least one method according to the invention.

Background

The external exhaust gas guide serves to reduce the emission of nitrogen oxides which are produced during the combustion of fuel in internal combustion engines, such as gasoline engines and diesel engines. Exhaust gas recirculation also helps to reduce breathing losses for gasoline engines, and thus also reduces fuel consumption during part load operation. For this purpose, part of the exhaust gases leaving the internal combustion engine is fed back into the intake manifold of the internal combustion engine via an exhaust gas feedback line. The inert exhaust gas mixed with fresh air hinders the rapid oxidation of the hydrocarbon molecules. Thus reducing the temperature spike when the fuel is combusted. The exhaust gas volume flow fed back is controlled by means of an exhaust gas feedback flap or an exhaust gas feedback valve.

However, over time, the amount of soot that is conducted back from the exhaust gas into the intake pipe mixes with the usual oil vapor, for example from the crankcase ventilation, to form a lubricating substance, which deposits in the intake elbow and on the inlet valve. This results in a significant narrowing of the intake cross section, which in turn reduces the engine power. If this happens unevenly between the cylinders of the internal combustion engine, it also causes a relative lack of air in the individual cylinders, which then produce more soot. This accelerates the deposit growth in the intake pipe even further.

In addition, soot deposition can cause exhaust gas feedback valves to seize. If the exhaust gas feedback valve is stuck open under heavy engine load, this results in a significant power loss, in which only a portion of the air quantity necessary for the desired torque is introduced into the cylinders of the internal combustion engine. If the valve is stuck in the closed state, an excessive amount of air is introduced into the cylinder during part load operation of the internal combustion engine. The engine control compensates for this with a larger injection quantity in order to achieve λ =1 and the firing angle is later with respect to the torque reduction. This results in increased fuel consumption and hotter exhaust gases due to deteriorated efficiency.

In addition to the possibility of limiting mechanical properties such as the displacement capacity and throughflow of the displacement zone, soot deposits can also lead to changes in the properties of the wall oil film in systems with intake pipe jets. The soot on the air inlet channel also entrains more fuel due to its larger surface area. Furthermore, severe and/or frequent intake pipe injections lead to the flushing of soot deposits, which, in the event of sudden large loosening, in the event of sudden or severe combustion or in the event of initiation of preignition (so-called knocking), can lead to damage in the cylinder and on the subsequent gas path. Furthermore, the greater fuel storage capacity in the intake manifold and on the soot surface on the intake valve disk of the internal combustion engine changes the amount of fuel in the wall oil film and, in particular in the case of dynamic load changes, significantly worsens the mixture formation and thus the exhaust gas.

Disclosure of Invention

The exhaust gas recirculation system is referred to below as an external exhaust gas recirculation system. An exhaust gas feedback system for an internal combustion engine has at least one fuel injection valve, the spray cone of which is directed toward the exhaust gas feedback line thereof. The fuel spray of the fuel injection valve can clean the exhaust gas feedback system. The dissolution properties of the fuel are used here in order to dissolve the soot deposits by wetting the soot-coated components and to feed them to the combustion mechanism. This enables the avoidance and/or removal of significant deposits in the exhaust gas recirculation system, and thus the exhaust gas deterioration and component damage of the internal combustion engine.

The spray cone of the fuel injection valve is preferably directed towards the beginning of the exhaust gas return line. The beginning of the exhaust gas feedback line is the region in which the exhaust gas feedback line branches off from the exhaust gas tract of the internal combustion engine. In this way, a spraying effect is ensured over the entire length of the exhaust gas feedback line.

A plurality of fuel injection valves may be distributed along the length of the exhaust gas feedback line in order to achieve a good spray effect even in the downstream region of the exhaust gas feedback line.

In one embodiment, the fuel injection valve is a conventional intake manifold injection valve, which is used, for example, for injecting fuel into an internal combustion engine using an intake manifold. Such an intake pipe injection valve can be used without structural changes for injecting fuel into the exhaust gas return line and is connected to a low-pressure fuel circuit. If the internal combustion engine has a valve for direct fuel injection, which is connected to a high-pressure fuel system (common rail), it is preferred in a further embodiment if the fuel injection valve of the exhaust gas feedback system is also connected to an existing high-pressure fuel system. For this purpose, the fuel injection valve is designed as a direct injection valve. In this way, a high fuel pressure is provided in the fuel injection valve, as a result of which a spray effect can be achieved over the longest possible path of the exhaust gas return line.

In a method for removing deposits or coatings from an exhaust gas feedback system, in particular an exhaust gas feedback line of an exhaust gas feedback system according to the invention, fuel is injected into the exhaust gas feedback line. In order to remove the deposits or the covering, it is necessary to have the liquid fuel contact the deposits. This is still ensured in the vicinity of the beam cone of the fuel injection valve. However, due to the heat of the exhaust gas and of the exhaust gas return line, the proportion of liquid fuel decreases with its length, since the fuel evaporates. In order to ensure that the liquid fuel fraction enters the exhaust gas return line as far as possible, it is therefore preferred that, when the fuel is injected, the fuel is cooled by an exhaust gas return cooling means which can be provided in the exhaust gas return system for cooling the exhaust gas.

In order to keep the exhaust gas temperature as low as possible, it is preferred that fuel is injected into the exhaust gas feedback line only during part-load operation of the internal combustion engine and/or only at early ignition angles of the internal combustion engine. In principle, it is also possible to perform the injection after a cold start of the internal combustion engine in its warm-running phase. But this results in increased hydrocarbon emissions.

The fuel injected into the exhaust gas feedback line enters the intake pipe of the internal combustion engine via the exhaust gas feedback line and is then combusted in the cylinders thereof. In order to take this additional fuel quantity into account in the injection quantity balancing of the cylinders, it is preferred that the fuel quantity provided for injection into the internal combustion engine is reduced by the fuel quantity already injected into the exhaust gas feedback line of the internal combustion engine. If the internal combustion engine has only one direct injection, the injected fuel quantity is subtracted from the direct injection quantity. For an internal combustion engine that performs a pure intake pipe injection, the amount of injected fuel is subtracted from the intake pipe injection amount. In so-called dual systems, however, it can be provided that the fuel injection takes place simultaneously via the intake manifold injector and the direct injector. It is then preferred that the amount of fuel to be injected via the intake manifold injector is first reduced by the amount of fuel already injected into the exhaust gas feedback line of the internal combustion engine. As long as the amount of fuel injected into the exhaust gas feedback line of the internal combustion engine is greater than the amount of fuel to be injected via the intake manifold injector, a margin amount remains. The difference amount is then deducted from the fuel quantity to be injected by the direct injection.

Since the mixture formation section in the exhaust gas return line extending to the cylinder inlet is comparatively long and the mixture formation is slow during the cleaning process, the fuel injection preferably does not take place in a dynamic process, such as scavenging. The injection is particularly preferably carried out during idling operation of the internal combustion engine and/or when the vehicle driven by the internal combustion engine is traveling at a constant speed. Furthermore, it is preferred to use a load prediction method, which can use navigation data of a vehicle driven by the internal combustion engine, for example, in order to determine a section of the internal combustion engine which is suitable for injecting fuel into the exhaust gas feedback line and is less ventilated in a suitable operating region.

In a preferred embodiment, the exhaust gas feedback flap or the exhaust gas feedback valve is opened or closed during the fuel injection. This movement particularly preferably takes place from one end position of the exhaust gas feedback flap or of the exhaust gas feedback valve into the other end position, i.e. from the fully closed position into the fully open position, or vice versa. In this way, deposits or coatings on the exhaust gas feedback flap or on the exhaust gas feedback valve can also be removed as completely as possible. In order to still be able to control the exhaust gas feedback rate, on the one hand, the exhaust gas feedback rate can be increased by means of a throttle flap in the intake tract of the internal combustion engine. On the other hand, a load pressure control may be employed to reduce the exhaust gas feedback rate. If a variable inlet valve gear, such as VVT or VVL, is present, the cylinder filling level can also be adjusted subsequently.

In a further preferred embodiment, the positions at which the flushing has been performed and the positions at which the flushing has not been performed are stored during the passage through the operating regions of the internal combustion engine and thus through the varying exhaust gas feedback rate and the varying flap position or valve position of the exhaust gas feedback mechanism. Subsequent injections into the exhaust gas feedback line are then triggered based on these stored data. This ensures that the exhaust gas feedback flap or valve is thoroughly wetted and cleaned without having to move the flap or valve against the values used. That is, the exhaust gas feedback flap is cleaned at the correspondingly adopted position without having to change the point of adoption.

If the fuel injection valve is arranged in an exhaust gas feedback system, this can be used not only for removing deposits or coatings, but also for normal operation of the internal combustion engine. In one embodiment of the method for operating an internal combustion engine, at least a portion of the quantity of fuel which is provided for injection into an intake manifold injector of the internal combustion engine is injected using a fuel injection valve if the temperature of the inlet channel of the internal combustion engine falls below a predeterminable temperature threshold value. If the inlet channel of the internal combustion engine is still too cold for the intake pipe injection at such low temperatures, which can lead to fuel entrainment and potential, it can be utilized here that the fuel is easily evaporated by the hot exhaust gases in the long mixture formation section of the exhaust gas return line and can be used for normal mixture formation.

In a further embodiment of the method, at least a portion of the fuel quantity intended for injection into the intake manifold injector and/or the direct injector in the internal combustion engine is injected with the fuel injection valve if the high concentration of the fuel to be injected exceeds a predetermined ethanol threshold. In the case of a high proportion of ethanol in the fuel and thus a high enthalpy of vaporization, both direct injection and intake pipe injection lead to wetting problems and thus to precipitation problems as a result of cooling. These problems can be avoided by moving the fuel quantity fraction towards the fuel injection valve of the exhaust gas feedback system.

The computer program is designed to carry out each step of one of the methods, in particular when the computer program runs on an electronic controller or computer. This enables the method to be carried out in a conventional controller without having to make constructional changes to it. For this purpose, the computer program is stored on a machine-readable storage medium. Transferring the computer program to a conventional electronic control unit results in an electronic control unit according to the invention which is designed to remove deposits or coatings from the exhaust gas feedback system of the internal combustion engine and/or to operate the internal combustion engine.

Drawings

Embodiments of the invention are illustrated in the drawings and will be described in detail in the following description.

FIG. 1 illustrates an exhaust gas feedback system according to an embodiment of the present invention;

FIG. 2 illustrates an exhaust gas feedback system according to another embodiment of the present disclosure;

FIG. 3 illustrates an exhaust gas feedback system according to yet another embodiment of the present invention;

FIG. 4 illustrates an exhaust gas feedback system according to yet another embodiment of the present invention.

Detailed Description

An internal combustion engine 1 of a motor vehicle, which is shown in fig. 1, has an intake pipe 2 and an exhaust gas tract 3. An exhaust gas feedback system 4 according to a first embodiment of the present invention connects the exhaust gas duct 3 with the intake pipe 2. The internal combustion engine 1 has four injection valves for the

direct injection pieces

11a, 11b, 11c, 11 d. These injection valves are connected to the high-pressure fuel system 5. A throttle flap 21 is provided in the intake pipe 2. The intake manifold 2 is connected to the internal combustion engine 1 via an inlet channel 22, wherein, upstream of each of the four cylinders of the internal combustion engine 1, an injection valve for an

intake manifold injector

24a, 24b, 24c, 24d is provided, which is connected to the low-pressure fuel system 6. The temperature sensor 23 measures the temperature in the input channel 22. At the beginning of the exhaust gas feedback line 41 of the exhaust gas feedback system 4, which leads into the exhaust gas tract 3, a fuel injection valve 43 is provided, which is designed as a direct injection valve, such that its spray cone is directed toward the exhaust gas feedback line 41. The fuel injection valve 43 is also connected to the high-pressure fuel system 5. An exhaust gas recirculation cooling mechanism 44 is provided in the exhaust gas recirculation line 41. The exhaust gas feedback valve 45 is designed to open and close the connection between the exhaust gas feedback line 41 and the inlet pipe 2. It is also controlled by the electronic control unit 7, as is the throttle flap 41.

In order to remove deposits or coatings from exhaust gas feedback line 41, in an exemplary embodiment of a method for removing deposits or coatings, fuel injection is interrupted (absetzen) by means of fuel injection valve 43. For this purpose, the route traveled by the internal combustion engine 1 during partial load operation at the previous ignition angle is identified by a method for load prediction in the near horizon by means of an auxiliary system and in the far horizon by means of a navigation system. The injected fuel or fuel spray or fuel-exhaust gas mixture is cooled by means of an exhaust gas recirculation cooling device 44 on the exhaust gas recirculation line 41, so that a rapid transition to the gaseous state is prevented, since it is advantageous for cleaning if the fuel is applied to the pollutants in liquid form. During fuel injection interruption, exhaust gas feedback valve 45 moves either from a fully open position to a fully closed position or from a fully closed position to a fully open position. In this way, it is possible to achieve as good a cleaning as possible of the exhaust gas feedback system including the exhaust gas feedback valve.

If the amount of fuel injected into the exhaust gas feedback line 41 is less than or equal to the amount of fuel to be injected through the

intake pipe injectors

24a, 24b, 24c, 24d, the amount of fuel to be injected through the

intake pipe injectors

24a, 24b, 24c, 24d is reduced by the amount of fuel already injected into the exhaust gas feedback line 41. As long as the amount of fuel injected into the exhaust gas feedback line 41 is greater than the amount of fuel to be injected through the

intake pipe injectors

24a, 24b, 24c, 24d, no fuel injection is performed through the

intake pipe injectors

24a, 24b, 24c, 24 d. The amount of fuel to be injected by the

direct injectors

11a, 11b, 11c, 11d is reduced by the difference between the amount of fuel already injected into the exhaust gas feedback line 41 and the amount of fuel to be injected by the

intake pipe injectors

24a, 24b, 24c, 24 d.

If, during operation of the internal combustion engine 1, a very low temperature in the inlet channel 22 is detected by means of the temperature sensor 23, in one exemplary embodiment of the method for operating the internal combustion engine 1, a partial quantity of fuel which is provided for injection by way of the

intake manifold injectors

24a, 24b, 24c, 24d is injected instead by means of the fuel injection valve 43.

If a high ethanol fraction of the fuel is detected in the fuel tank of the internal combustion engine 1 by means of an ethanol sensor, not shown, both the portion of the fuel quantity to be injected by the

direct injectors

11a, 11b, 11c, 11d and the portion of the fuel quantity to be injected by the

intake manifold injectors

24a, 24b, 24c, 24d are injected instead by means of the fuel injection valve 43. In this way, the problems of fuel entrainment (einlagering) and of trapping (vorlingung) in the region of the feed channel and in the cylinders of the internal combustion engine 1 can be overcome.

In the second exemplary embodiment of exhaust gas feedback system 4 shown in fig. 2, fuel injection valve 43 is designed as an intake manifold injection valve connected to the same low-pressure fuel system 6, which also supplies

intake manifold injectors

24a, 24b, 24c, 24d with fuel.

In the third exemplary embodiment of the exhaust gas recirculation system 4, the internal combustion engine 1 has no injection valves for the

direct injectors

11a, 11b, 11c, 11d and no high-pressure fuel system 5. This is shown in fig. 3. Fuel injection valve 43 is also designed in this embodiment as an intake pipe injection valve connected to low-pressure fuel system 6. If in one exemplary embodiment of the method for removing deposits or coatings the fuel injection is interrupted by means of a fuel injection valve 43 designed as an intake manifold injection valve, the amount of fuel to be injected via the

intake manifold injectors

24a, 24b, 24c, 24d is reduced by the amount of fuel already injected into the exhaust gas feedback line 41.

A fourth embodiment of an exhaust gas feedback system 4 is shown in fig. 4. It differs from the first embodiment in that it does not have the low-pressure fuel system 6, nor the

intake pipe injectors

24a, 24b, 24c, 24 d. The fuel injection valve 43 of the exhaust gas feedback system 4 can be operated in the same manner as the exhaust gas feedback system 4 of the first embodiment.

Claims

1. A method for removing deposits or coatings from an exhaust gas feedback system (4) of an internal combustion engine (1), characterized in that fuel is injected into an exhaust gas feedback line (41) of the exhaust gas feedback system (4), wherein fuel is injected into a beginning (42) of the exhaust gas feedback line (41), wherein a fuel quantity specified for injection into the internal combustion engine (1) is reduced by a fuel quantity already injected into the exhaust gas feedback line (41) of the internal combustion engine (1), and wherein, when a fuel injection is specified simultaneously by means of an intake pipe injector (24 a, 24b, 24c, 24 d) and a direct injector (11 a, 11b, 11c, 11 d), the fuel quantity to be injected by means of the intake pipe injector (24 a, 24b, 24c, 24 d) is first reduced by the fuel quantity already injected into the exhaust gas feedback line (41) of the internal combustion engine (1), provided that the quantity of fuel injected into the exhaust gas feedback line (41) of the internal combustion engine (1) is greater than the quantity of fuel to be injected by way of the intake manifold injectors (24 a, 24b, 24c, 24 d) and that the quantity of fuel to be injected by way of the direct injectors (11 a, 11b, 11c, 11 d) is reduced by the remaining difference quantity, which is the difference between the quantity of fuel injected into the exhaust gas feedback line (41) of the internal combustion engine (1) and the quantity of fuel to be injected by way of the intake manifold injectors (24 a, 24b, 24c, 24 d).

2. A method as claimed in claim 1, characterized in that the fuel injection is carried out only during part-load operation of the internal combustion engine (1) and/or only at early ignition angles of the internal combustion engine (1).

3. A method according to claim 1 or 2, characterized in that the exhaust gas feedback flap or the exhaust gas feedback valve (45) is made to open or close during fuel injection.

4. Method according to claim 1 or 2, characterized in that the internal combustion engine (1) has an exhaust gas feedback system (4) with at least one fuel injection valve (43) whose spray cone is directed towards its exhaust gas feedback line (41), wherein the spray cone of the fuel injection valve (43) is directed towards the beginning (42) of the exhaust gas feedback line (41).

5. A method according to claim 4, characterized in that the fuel injection valve (43) is connected to a low-pressure fuel system (6) of the internal combustion engine (1).

6. The method as claimed in claim 4, characterized in that the fuel injection valve (43) is connected to a high-pressure fuel system (5) of the internal combustion engine (1).

7. A method according to claim 4, characterized in that the fuel injection valve (43) is arranged between the beginning (42) of the exhaust gas feedback line (41) and an exhaust gas feedback cooling mechanism (44).

8. A method according to claim 4, characterized in that the fuel injection valve (43) is arranged between the beginning (42) of the exhaust gas feedback line (41) and an exhaust gas feedback cooling mechanism (44), and that the fed back exhaust gas is cooled in the exhaust gas feedback cooling mechanism (44).

9. A method for operating an internal combustion engine (1) having an exhaust gas feedback system (4) having at least one fuel injection valve (43) with a spray cone directed towards its exhaust gas feedback line (41), wherein the spray cone of the fuel injection valve (43) is directed towards a beginning (42) of the exhaust gas feedback line (41), wherein at least a portion of a fuel quantity intended for an intake pipe injector (24 a, 24b, 24c, 24 d) into the internal combustion engine (1) is injected with the fuel injection valve (43) if a temperature of an inlet channel (22) of the internal combustion engine (1) is below a predeterminable temperature threshold value.

10. A method according to claim 9, characterized in that the fuel injection valve (43) is connected to a low-pressure fuel system (6) of the internal combustion engine (1).

11. The method as claimed in claim 9, characterized in that the fuel injection valve (43) is connected to a high-pressure fuel system (5) of the internal combustion engine (1).

12. A method according to claim 9, characterized in that the fuel injection valve (43) is arranged between the beginning (42) of the exhaust gas feedback line (41) and an exhaust gas feedback cooling mechanism (44).

13. A method for operating an internal combustion engine (1) having an exhaust gas feedback system (4) having at least one fuel injection valve (43) with a spray cone directed towards its exhaust gas feedback line (41), wherein the spray cone of the fuel injection valve (43) is directed towards the beginning (42) of the exhaust gas feedback line (41), wherein at least a portion of the fuel quantity of an intake manifold injector (24 a, 24b, 24c, 24 d) and/or a direct injector (11 a, 11b, 11c, 11 d) intended for injection into the internal combustion engine (1) is injected with the fuel injection valve (43) if the ethanol concentration of the fuel to be injected exceeds a predeterminable ethanol threshold value.

14. The method as claimed in claim 13, characterized in that the fuel injection valve (43) is connected to a low-pressure fuel system (6) of the internal combustion engine (1).

15. The method as claimed in claim 13, characterized in that the fuel injection valve (43) is connected to a high-pressure fuel system (5) of the internal combustion engine (1).

16. Method according to claim 13, characterized in that the fuel injection valve (43) is arranged between the beginning (42) of the exhaust gas feedback line (41) and an exhaust gas feedback cooling mechanism (44).

17. A machine-readable storage medium on which is stored a computer program designed to implement each step of the method according to any one of claims 1 to 16.

18. An electronic control unit (7) which is designed to remove deposits or coatings from an exhaust gas feedback system (4) of an internal combustion engine (1) by means of a method according to any one of claims 1 to 8 and/or to operate the internal combustion engine (1) by means of a method according to any one of claims 9 to 16.