DE102011003912B4 - Device and method for metering a liquid into the exhaust system of an internal combustion engine - Google Patents

Abstract

Device for metering a liquid (12) to support the exhaust gas after-treatment into an exhaust line (8) of an internal combustion engine (5), the liquid (12) being metered into the exhaust line (8) of the internal combustion engine (5) by means of a nozzle arrangement (30), wherein the nozzle arrangement has a valve (31) and wherein metering of the liquid (12) to the nozzle arrangement (30) is controlled or regulated by a metering pump (20), wherein the valve (31) when the metering pump (20) is activated Buzzing operation periodically opens and closes, characterized in that a pulsation damper (22) is arranged between the metering pump (20) and the nozzle arrangement (30).

Description

State of the art

The invention relates to a device for dosing a liquid into the exhaust system of an internal combustion engine according to the preamble of claim 1 and a method according to the preamble of claim 9.

Due to exhaust gas legislation that is becoming ever more stringent, it is nowadays hardly possible to achieve the limit values in relation to the pollutants in the exhaust gas of an internal combustion engine solely with internal engine measures. For this reason, exhaust gas aftertreatment devices, for example catalytic converters and filters, arranged in the exhaust system of the internal combustion engine have become established in internal combustion engines, in particular in internal combustion engines of vehicles. In self-igniting internal combustion engines in particular, exhaust gas after-treatment devices are increasingly being used, in which a liquid is metered into the exhaust tract of the internal combustion engine to support the exhaust gas after-treatment. Examples include the dosing of fuel to regenerate a particle filter or the dosing of aqueous urea solution in catalytic converters for the selective reduction of nitrogen oxides. For the thermal regeneration of particle filters, for example, the exhaust gas temperature of internal combustion engines is raised so that the soot contained in the particle filter burns off in a controlled manner. If this exhaust gas temperature increase is not possible through engine measures, an additional injector doses fuel into the exhaust gas, which reacts catalytically on an oxidation catalytic converter, releasing the heat required to increase the temperature.

Out of DE 10 2007 016 004 A1 a dosing device is known in which a dosing pump doses an exhaust aftertreatment agent into an exhaust system of an internal combustion engine.

Out of DE 10 2006 057 425 A1 a device for metered injection of a fluid into an exhaust line of an internal combustion engine is known, in which an injection valve working in buzzing mode meters the supplied fluid into the exhaust line of the internal combustion engine.

From the DE 10 2005 034 704 A1 a device and a method for regenerating a particle filter are known.

The DE 10 2005 037 150 A1 describes a device for metering a reducing agent, preferably for commercial vehicle applications.

From the DE 10 2004 050 023 A1 a device for the metered injection of a reducing agent into the exhaust tract of an internal combustion engine is also known.

epiphany

In contrast, the device according to the invention with the features mentioned in claim 1 offers the advantage that the metering of the liquid is controlled or regulated by a metering pump, so that the pressure is generated and the metering of the liquid takes place at one point, with the injection valve pumping the liquid in buzzing mode into metered into the exhaust system, which enables the metering of small amounts of liquid into the exhaust system and achieves very fine atomization. The metering is not or only slightly disturbed by pressure fluctuations, for example from a supply device upstream of the metering pump, in particular a low-pressure circuit of a fuel injection system. This leads to a simplified system concept with simple hydraulic behavior, an extended operating range in terms of dosed quantity and increased dosing accuracy. The costs are reduced, for example, due to the omission of a metering unit and the application effort on the internal combustion engine is lower due to the simple hydraulic behavior. For example, the pressure fluctuations caused by two or more flow-limiting valves with correspondingly complex hydraulic behavior do not have to be taken into account in the application. A pulsation damper is arranged between the reservoir and the nozzle arrangement, in particular between the metering pump and the valve. Damping the pressure fluctuations between the reservoir or a low-pressure circuit of a fuel injection system and the metering pump further increases the metering quantity accuracy of the metering pump. A damping of the pressure fluctuations between the dosing pump and the valve is particularly advantageous since the chattering operation of the valve can be disturbed by pressure fluctuations.

Advantageous developments and improvements of the device specified in claim 1 and of the method specified in claim 9 are possible as a result of the measures listed in the dependent claims.

A further advantageous development consists in the fact that the nozzle arrangement has a pressure-controlled valve which, when an opening pressure (p _O ) is reached or exceeded, releases metering of the liquid into the exhaust system of the internal combustion engine. A pressure controlled The valve can be designed without an electrical controller and is therefore particularly simple and inexpensive.

It is particularly advantageous if the opening pressure (p _Ö ) of the valve is above a pressure in a reservoir upstream of the metering pump or above a pressure in a low-pressure circuit upstream of the metering pump, for example the low-pressure circuit of a fuel injection system. As a result, the valve only opens when the pressure in the reservoir or low-pressure circuit increases due to the dosing pump. In this way, malfunctions and undesired dosing through the valve can be avoided.

A further advantageous development of the device is that the dosing pump does not deliver any liquid in the event of a malfunction, in particular in the event of a permanent current supply or an electrical short circuit. This further development prevents the liquid escaping into the exhaust system and from there into the environment in the event of a defect or a malfunction. If, in the event of a malfunction, no more liquid is made available by the metering pump, the injection valve remains closed so that no liquid is undesirably metered into the exhaust system. In this way, a “fail safe” function of the device can also be easily implemented, so that no liquid is metered into the exhaust system of the internal combustion engine if the metering pump fails.

In order to increase the dosing accuracy, it is advantageous if the quantity of liquid delivered by the pump is independent of the back pressure in the exhaust line or the metered quantity of liquid is dependent solely on the actuation of the pump. By using a controllable piston pump as the dosing pump, metering and dosing can advantageously be implemented in one unit, the dosed amount of liquid then being exclusively dependent on the control duration of the dosing pump.

It is particularly advantageous if the metering pump pressurizes the liquid at a frequency of 1 to 10 Hertz and/or periodically opens and closes the injection valve at a frequency of approximately 1000 Hz. An activation frequency of the dosing pump in this frequency range ensures that the dosing pump delivers the quantities of liquid that are typically required in exhaust aftertreatment to the injection valve at a constant pressure. When the injection valve buzzes at approx. 1000 Hz, the amount of liquid provided by the metering pump is dosed finely and in small portions into the exhaust gas system and can thus be evenly distributed in the exhaust gas flow without deposits forming on the injection valve or in the exhaust gas system.

character list

• 1 represents a device according to the invention for metering a liquid into the exhaust line of an internal combustion engine.
• 2 represents an alternative embodiment of the device according to the invention for metering a liquid into the exhaust line of an internal combustion engine.
• 3 shows a diagram in which the amount of liquid provided by the metering pump is shown as a function of the exhaust gas back pressure.
• 4 shows the pressure curve of the liquid at the outlet of the dosing pump depending on the control of the dosing pump.
• 5 shows the pressure curve at the injection valve as a function of the control of the metering pump with the injection valve opening and closing periodically in chattering mode.

Brief description of the drawings

The invention and advantageous configurations according to the features of the other claims are explained in more detail below with reference to the exemplary embodiments illustrated in the drawings. In the 1 and 2 Identical components or components with the same function are identified by the same reference symbols.

In 1 a first exemplary embodiment of the device according to the invention is shown. A reservoir 10 for storing a liquid 12 is connected to a filter 13 via a connecting line 41 . The filter 13 is connected to a metering pump 20 via a second connecting line 45 , a pressure sensor 24 being arranged on the connecting line 45 . Another connecting line 46 leads from an outlet 21 of the metering pump 20 to a nozzle arrangement 30 , for example an injection valve 31 , a pulsation damper 22 and a pressure sensor 26 being arranged on the connecting line 46 . The injection valve 31 is arranged on an exhaust line 8 of an internal combustion engine 5 .

If the liquid 12 is to be metered into the exhaust line 8 of the internal combustion engine 5 to support the exhaust aftertreatment, the metering pump 20 draws in the liquid 12 from the reservoir 10 via the connecting line 41, the liquid 12 , for example aqueous urea solution or fuel, being cleaned in the filter 13 and flowing to the metering pump 20 via the connecting line 45 . The metering pump 20 puts the liquid 12 under a pressure (p), the pressure curve generated over a period of time (t) being generated by the metering pump 20 at the outlet 21 of the metering pump as shown in FIG 4 shown is approximately "rectangular", i.e. when the metering pump 20 is activated, there is a steep rise in pressure up to a peak pressure level (p _p ) of the metering pump 20, with this peak pressure level (p _p ) largely being maintained until the end of the activation of the metering pump 20, whereupon the pressure (p) drops sharply again. In addition to generating pressure, the metering pump 20 has the function of metering the amount of liquid 12 that is to be metered into the exhaust line 8 . This measurement takes place via the control duration of the dosing pump 20.

Due to the peak pressure level (p _p ) generated in the metering pump 20 , a hydraulic force acts on the injection valve 31 which is greater than a closing force which acts on a closing element 32 of the injection valve 31 . By overcoming the locking force of the closing element 32 of the injection valve 31, the injection valve 31 reaches an opening pressure (p _Ö ), the injection valve 31 opening and injecting the liquid 12 and spray conditioning the liquid 12 when it is metered into the exhaust system. As a result of the opening of the injection valve 31, the pressure (p) at the injection valve 31 briefly drops slightly to a closing pressure ( _ps ), as a result of which the closing element 32 of the injection valve 31 closes again. The closing of the closing element 32 causes the pressure (p) to rise again, as a result of which a characteristic, periodic opening and closing of the injection valve 31 occurs, which is referred to as chattering operation. The pressure profile of such a buzzing operation as a function of the activation of the metering pump 20 is in 5 plotted against time (t). Due to the rapid, periodic opening and closing of the injection valve 31 , small amounts of the liquid 12 are metered finely into the exhaust system 8 of the internal combustion engine 5 . It is also characteristic of the metering pump 20 that the delivered quantity (Q') of the liquid 12, as in 3 shown, is independent of the back pressure (Δp) in the exhaust line 8 . A quantity control of the dosing pump 20 can be carried out by means of pulse width and frequency modulation. When the metering pump 20 is not activated, no pressure is built up, so that the injection valve 31 is closed when the metering pump 20 is not activated.

A pulsation damper 22 is arranged on the connecting line 46, which connects the metering pump 20 to the injection valve 31, which dampens pressure fluctuations which arise as a result of the pressure generation in the metering pump 20 and/or as a result of the metering of the liquid 12 through the injection valve 31. In this case, the injection valve 31 is designed as an outwardly opening, spring-loaded poppet valve.

A mechanical guidance of the closing element 32 can be dispensed with if the closing element 32 of the injection valve 31 is positioned by a valve spring and is centered by a flow of the liquid 12 through the injection valve 31 . The individual components of the injection valve 31 are made of metal. Since reliable buzzing operation of the injection valve 31 is only possible in a relatively narrow pressure range, the pulsation damper 22 can prevent this narrow pressure range from being left. The pulsation damper 22 is designed as a membrane damper, pneumatically or as a hydraulic volume. The pulsation damper is preferably arranged in the immediate vicinity of the outlet 21 of the metering pump 20 . Alternatively, the pulsation damper 22 can also be integrated into the metering pump 20 .

In addition, the pressure (p) in line 45 is measured via a pressure sensor 24 arranged on line 45 and in line 46 via a pressure sensor 26 . The function and performance of the dosing pump 20 can be controlled via the two pressure sensors 24 , 26 . A malfunction or a failure of the injection valve 31 can also be detected by the pressure sensor 26 . The injection valve 31 can be air- or water-cooled.

Alternatively, in a simpler embodiment of the device, the pulsation damper 22 and at least one of the pressure sensors 24, 26 can also be omitted. In particular, if the pulsation damper 22 is omitted, it is advantageous if the length of the line 46 between the metering pump 20 and the injection valve 31 is as short as possible in order to keep pressure waves and associated pressure fluctuations as low as possible. As an alternative to the illustrated embodiment in 1 the filter 13 between the dosing pump 20 and the reservoir 10 can also be omitted, the liquid 12 then being sucked in directly by the dosing pump 20 from the reservoir 10 via the line 45 . The metering pump 20 is preferably designed as a controllable piston pump, for example as an electromagnetically operated oscillating piston pump. Alternatively, however, other pumps that work according to the displacement principle can also be used, in particular pumps that 4 can display the pressure profile shown. Alternatively, the injection valve 31 can also be implemented as an inwardly opening poppet valve or in other embodiments. Individual components of the injection valve 31 can also be made of non-metallic materials, in particular a suitable ceramic, a polymer or a composite material. In particularly simple embodiments of the device, an uncooled injection valve 31 can also be used.

2 shows an alternative embodiment of the device according to the invention. A low-pressure circuit 15 of a fuel injection system includes a reservoir 10 for storing a liquid 12 and a pre-supply pump 14. The reservoir is connected to a filter 13 via a connecting line 41. Another connecting line 42 leads from the filter 13 to the pre-supply pump 14 of the low-pressure circuit 15 of the fuel injection system. The pre-supply pump 14 is connected to a branching point 52 via a line 43 . A connecting line 45 leads from the branching point 52 to the metering pump 20 , a pressure sensor 24 being arranged on the connecting line 45 . A connecting line 44 leads from the branching point 52 to a high-pressure area 18 of the fuel injection system, the high-pressure area 18 comprising a high-pressure pump, a pressure accumulator and at least one fuel injector in a known embodiment. The high-pressure area 18 is connected to the reservoir 10 via a return line 49 . Another connecting line 46 leads from the outlet 21 of the metering pump 20 to the injection valve 31 , a pulsation damper 22 and a pressure sensor 26 being arranged on the connecting line 46 . The injection valve 31 is arranged on the exhaust line 8 of the internal combustion engine 5 .

The liquid 12, in particular a fuel, is sucked out of the reservoir 10 by the pre-supply pump 14 and flows through the connecting line 41 into the filter 13, where particles and impurities are filtered out of the liquid 12. From there, the liquid 12 flows via the connecting line 42 to the pre-supply pump 14, where the liquid is compressed and conveyed through the line 43 to the branching point 52. A first partial flow of the liquid flows from the branching point 52 via the connecting line 44 to the high-pressure area 18 of the fuel injection system, while a second partial flow flows through the connecting line 45 to the metering pump 20 . A pressure sensor 24 is arranged on the connecting line 45 and is used to measure a pressure of the liquid 12 in the connecting line 45 . The pressure generation of the metering pump 20 is analogous to the explanations 1 .

Alternatively, the pre-supply pump 14 can also be arranged between the reservoir 10 and the filter 13 in the low-pressure circuit 15 . Alternatively, it is also possible for the pre-supply pump 14 to include a filter 13, in particular on the suction side. As a further alternative, the pre-supply pump 14 can also have two outlets, one outlet of the pre-supply pump 14 then being connected via a connecting line 45 to the metering pump 20 and another outlet of the pre-supply pump 14 being connected via the connecting line 44 to the high-pressure region 18 of the fuel injection system, in particular to a High-pressure pump is connected. Alternatively, the connecting line 45 can also be connected to a low-pressure outlet of a high-pressure pump belonging to the high-pressure region 18, with an additional pulsation damper being able to be arranged on the connecting line 45 in order to dampen the pressure fluctuations of the high-pressure pump.

Claims (9)

Device for metering a liquid (12) to support the exhaust gas after-treatment into an exhaust line (8) of an internal combustion engine (5), the liquid (12) being metered into the exhaust line (8) of the internal combustion engine (5) by means of a nozzle arrangement (30), wherein the nozzle arrangement has a valve (31) and wherein metering of the liquid (12) to the nozzle arrangement (30) is controlled or regulated by a metering pump (20), wherein the valve (31) when the metering pump (20) is activated Buzzing operation periodically opens and closes, characterized in that a pulsation damper (22) is arranged between the metering pump (20) and the nozzle arrangement (30). device after claim 1 , characterized in that the nozzle arrangement (30) has a pressure-controlled valve (31) which releases metering of the liquid (12) into the exhaust system (8) of the internal combustion engine (5) when an opening pressure (p _Ö ) is reached or exceeded. device after claim 2 , characterized in that the opening pressure (p _Ö ) of the valve (31) is above a pressure in a storage tank (10) upstream of the metering pump (20) or above a pressure in a low-pressure circuit (15 ) lies. device after claim 3 , characterized in that the low-pressure circuit (15) is the low-pressure circuit of a fuel injection system. Device according to one of Claims 1 until 4 , characterized in that the metering pump (20) does not deliver any liquid (12) in the event of a malfunction. Device according to one of Claims 1 until 5 , characterized in that the quantity of liquid (12) conveyed by the metering pump (20) is independent of the back pressure in the exhaust line (8) or the metered quantity of liquid (12) depends exclusively on the control of the metering pump (20). Device according to one of Claims 1 until 6 , characterized in that a quantity control of the metering pump (20) is carried out by means of a pulse width or a frequency modulation. Device according to one of Claims 1 until 7 , characterized in that pressure sensors (24) are provided, which serve to regulate or diagnose the metering pump. Method for metering a liquid (12) to support the exhaust gas aftertreatment into an exhaust system (8) of an internal combustion engine (5), the liquid (12) being metered into the exhaust system (8) of the internal combustion engine (5) by means of a nozzle arrangement (30), characterized in that metering of the liquid (12) is controlled or regulated by a metering pump (20), a pulsation damper (22) being arranged between the metering pump (20) and the nozzle arrangement (30).

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