DE102007026944A1 - A urea metering system for an internal combustion engine and a method and apparatus for metering urea by means of the urea metering system - Google Patents

Abstract

An internal combustion engine (14) comprises at least one cylinder (Z1) with a combustion chamber (9) and an exhaust gas tract (4) which communicates with the combustion chamber (9) as a function of a switching position of a gas outlet valve (13). A urea metering system for the internal combustion engine (14) comprises a urea injection valve (54) for metering urea into the exhaust tract (4), a urea tank (40) from which urea can be sent to the urea injection valve (54) via a urea line (41), and an air compressor (50) coupled to the urea tank (40) such that an overpressure in the urea tank (40) can be created with the air compressor (50).

Description

The The invention relates to a urea metering system for an internal combustion engine. The internal combustion engine comprises a cylinder with a combustion chamber and an exhaust tract. The exhaust tract communicates depending on a switching position of a gas outlet valve with the combustion chamber. The urea metering system includes a urea injector for metering of urea in the exhaust tract. Further, the urea metering system includes a urea tank from which over a urea line urea to the urea injection valve can be directed. Furthermore, the invention relates to a method and a device for metering urea by means of the urea metering system.

to Reduction of a nitrogen oxide content in the exhaust gas of an internal combustion engine can an exhaust aftertreatment with aqueous urea solution and a SCR catalyst performed become. The watery urea solution can also be referred to as urea. For exhaust aftertreatment becomes the watery urea solution with a liquid pump pumped to a urea injection valve, which is the urea solution upstream of the SCR catalyst in an exhaust gas stream in an exhaust tract of the internal combustion engine attaches. The urea solution reacts in the hot Exhaust gas flow to ammonia and carbon dioxide. In the SCR catalyst then the ammonia reacts with the nitrogen oxide mixture of the exhaust gas to nitrogen and water.

The The object of the invention is a urea metering system and a method and a device for metering urea by means of the urea metering system to create, the or a particularly favorable Metering urea in an exhaust tract of an internal combustion engine allows.

The Task is solved by the characteristics of the independent Claims. Advantageous embodiments of the invention are specified in the subclaims.

The Invention is characterized according to a first Aspect of the invention by a urea metering system for an internal combustion engine. The internal combustion engine comprises at least one cylinder with a Combustion chamber and an exhaust tract. The exhaust tract communicates depending on a switching position of a gas outlet valve with the combustion chamber. The urea metering system includes a urea injector for Metering of urea into the exhaust tract, a urea tank and an air compressor. From the urea tank can via a urea line Urea be directed to the urea injection valve. The air compressor is so coupled with the urea tank, that with the air compressor an overpressure can be generated in the urea tank.

The overpressure in the urea tank, for example, to an ambient air pressure the urea tank are produced and / or against an air pressure in the Exhaust tract into which the urea is metered.

This contributes a simple metering of the urea in the exhaust tract at. Further This can help pressurizing the urea tank the urea tank is tightly closed. Furthermore, the urea tank serve as Druckspei cher and so a duration of the air compressor to reduce the pressure. This can help the air compressor with a 2-point control to operate. The urea tank can be pressurized by, for example be applied up to 8 bar.

In an advantageous embodiment of the first aspect of the invention For example, the urea metering system includes a vent line. The vent line is for rinsing the urea line coupled to the air compressor and the urea injection valve. This can become a reliable one Operation of the urea metering system, for example, can Prevents urea in the urea line too strongly heated and then clots and / or that the urea cools down too much and freezes. Both the clotting and the freezing of urea can be a goodness reduce the exhaust aftertreatment by means of the urea.

In a further advantageous embodiment of the first aspect of The invention comprises the urea-metering system for connecting a external compressed air line a compressed air connection. The compressed air connection is coupled to the air compressor. At the compressed air connection For example, an attachment for inflating example of a car tire and / or an inflatable boat are placed. This makes possible, the air compressor outside of the regular Use of the urea metering system advantageous to use.

The Invention is characterized according to a second Aspect of the invention by a method and an apparatus for Metering of urea by means of the urea metering system. there becomes the overpressure produced in the urea tank. The urea is made by means of the overpressure passed in the urea tank to the urea injection valve.

In an advantageous embodiment of the second aspect of the invention the urea injector is via the vent line so pressurized that the urea passes through the urea line back rinsed in the urea tank becomes.

In a further advantageous embodiment of the second aspect of Invention, the urea injection valve via the vent line so pressurized to urea through the urea line back rinsed in the urea tank when the internal combustion engine is switched off.

embodiments The invention are explained in more detail below with reference to schematic drawings.

It demonstrate:

1 a first view of an internal combustion engine,

2 a second view of the internal combustion engine with a urea-metering system,

3 a flow chart of a program for metering urea by means of the urea metering system.

elements same construction or function are cross-figurative with the same Reference number marked.

An internal combustion engine 14 ( 1 ) comprises an intake tract 1 , an engine block 2 , a cylinder head 3 and an exhaust tract 4 , The intake tract 1 preferably comprises a throttle valve 5 , a collector 6 and a suction tube 7 leading to a cylinder Z1-Z4 via an inlet channel into a combustion chamber 9 of the engine block 2 is guided. The combustion chamber 9 communicates depending on a switching position of a gas inlet valve 12 or a gas outlet valve 13 with the intake tract 1 or with the exhaust gas tract 4 , The engine block 2 includes a crankshaft 8th , which has a connecting rod 10 with a piston 11 of the cylinder Z1-Z4 is coupled. The internal combustion engine 14 preferably comprises further cylinders Z1-Z4. The internal combustion engine 14 is preferably arranged in a motor vehicle. The motor vehicle is preferably a passenger vehicle.

In the cylinder head 3 is preferably a fuel injection valve 18 arranged. If the internal combustion engine 14 is not a diesel engine, so preferably each cylinder Z1-Z4 are each assigned a spark plug. Alternatively, the fuel injection valve 18 also in the intake manifold 7 be arranged. A fuel return line 44 allows for recirculation of unappropriated fuel from the fuel injector 18 towards a fuel tank.

The exhaust tract 4 includes a soot particle filter 21 and at least one SCR catalyst 23 , To urea urea protrudes a urea injection valve 54 ( 2 ) in the exhaust tract 4 downstream of the soot particle filter 21 and upstream of the SCR catalyst 23 , Downstream of the urea injection valve 54 and upstream of the SCR catalyst 23 Preferably, a mixing device for mixing the metered urea with the exhaust gas is arranged. In addition to the SCR catalyst 23 may be upstream of the SCR catalyst 23 and a hydrolysis catalyst downstream of the mixing device and downstream of the SCR catalyst 23 An oxidation catalyst may be provided.

Furthermore, the exhaust tract 4 preferably assigned to a urea-metering system ( 2 ). The urea-metering system comprises a urea tank 40 for picking up the urea, the urea injection valve 54 and the air compressor 50 , The air compressor 50 is like that with the urea tank 40 coupled that air in the urea tank 40 by means of the air compressor 50 can be pressurized so that the air pressure in the urea tank 40 an overpressure with respect to an environment of the urea tank 40 and / or to a pressure in the exhaust tract 4 downstream of the soot particle filter 21 and upstream of the SCR catalyst 23 represents. The overpressure in the urea tank 40 causes the urea from the urea tank 40 via a urea line 14 to the urea injection valve 54 is directed. By appropriate activation of the urea injection valve 54 can then urea the exhaust tract 4 be measured. The overpressure in the urea tank 40 is preferably dependent on a switching position of a urea valve 52 set. The pumping of urea from the urea tank 40 towards the urea injector 54 contributes to an advantageous metering of the urea, for example because even in the case where almost all of the urea in the urea tank 40 frozen, a liquid residue of urea to the urea injection valve 54 is directed.

Furthermore, this can put pressure on the urea tank 40 help the urea tank 40 is tightly closed.

Furthermore, the urea tank 40 serve as an accumulator and so a duration of the air compressor 50 to reduce the pressure. This can help the air compressor 50 operate with a 2-point control. The urea tank 40 can be applied with a pressure of, for example, up to 8 bar. The one for the urea tank 40 intended pressure should be in the construction of the urea tank 40 be taken into account. If the urea tank 40 designed to be particularly stable, this can also contribute to urea does not escape in an accident. If the urea in the urea tank 40 freezes, the frost layer dissolves better from a wall of the urea tank 40 when it is under pressure.

For venting the urea line 41 is a vent line 56 intended. Depending on a switching position of a vent valve 58 can then air out of the air compressor 50 be used to at least partially remove the urea from the urea injection valve 54 and over the urea line 41 towards the urea tank 40 to rinse back. This is particularly advantageous when a motor vehicle in which the internal combustion engine 14 is arranged, for example, in the summer at high temperatures or, for example, in winter at very low temperatures is turned off. This can prevent the urea in the urea line 41 due to the heat clots or freezes due to the cold. This can contribute to reliable operation of the urea metering system and low wear of the urea metering system. The freezing of the urea impedes or prevents the metering of the urea into the exhaust tract 4 , This reduces or prevents the exhaust aftertreatment by means of the urea. This leads to an increase in harmful pollutant emissions. The clotting of urea can also help to reduce or completely prevent the effect of exhaust aftertreatment with urea.

The air compressor 50 can also be used to generate compressed air outside the engine 14 , For example, outside the motor vehicle can be used. For this purpose, preferably a compressed air outlet 60 provided on which, for example, an attachment for pumping up a tire and / or a rubber boat is provided.

A control device 25 is provided, the sensors are assigned, which detect different parameters and each determine the value of the measured variable. The control device 25 determined depending on at least one of the measured variables at least one manipulated variable, which are then converted into one or more control signals for controlling the actuators by means of corresponding actuators. The control device 25 can also be used as a device for operating the internal combustion engine 14 be designated. In particular, the control device 25 be referred to as a device for metering the urea.

The sensors are, for example, a pedal position transmitter 26 , the accelerator pedal position of an accelerator pedal 27 detected, an air mass sensor 28 , the air mass flow upstream of the throttle 5 detected, a temperature sensor 32 sensing an intake air temperature, an intake manifold pressure sensor 34 that produces a manifold pressure in the collector 6 detected, a crankshaft angle sensor 36 , which detects a crankshaft angle, then a speed of the internal combustion engine 14 can be assigned, a urea tank pressure sensor 46 for detecting an air pressure in the urea tank 40 , Furthermore, an exhaust gas probe 38 provided, for example, downstream of the SCR catalyst 23 is arranged and detects, for example, a nitrogen oxide content and / or a urea content of the exhaust gas.

ever according to embodiment The invention may be any subset of said sensors be present or it can also additional Sensors be present.

The actuators are, for example, the throttle 5 , the gas inlet and outlet valves 12 . 13 , the fuel injection valve 18 , the urea injector 54 , the urea valve 52 , the air compressor 50 , the vent valve 58 and / or optionally the spark plug.

On a storage medium of the control device 25 is preferably a program ( 3 ) for metering urea by means of the urea metering system.

The Program is preferably started in a step S1 by if necessary variables are initialized.

In a step S2, during a urea metering operation INJ, the urea becomes the exhaust gas tract 4 meted out. A urea mass, which during the urea metering process INJ the exhaust tract 4 is measured, is preferably by means of a corresponding program for determining the urea mass of the control device 25 determined. Preferably, the urea mass to be metered is determined as a function of a nitrogen oxide content of the exhaust gas, for example as a function of a measurement signal of the exhaust gas probe 38 , For example, on the storage medium of the control device 25 a map can be stored, on the basis of which, depending on the nitrogen oxide content of the exhaust gas, the corresponding urea mass can be read out. The map and possibly other maps can be recorded, for example, on a motor test bench. As an alternative to the characteristic map, a model calculation can be filed on the storage medium, on the basis of which the urea mass for the urea metering process INJ can be determined.

Preferably, for example, when the internal combustion engine 14 is switched off, by means of a deactivation instruction DEACT in a step S3 venting of the urea line 41 initiated.

Then in a step S4 is preferred way the vent valve 58 opened and the urea valve 52 closed. This causes compressed air in the urea injection valve 54 is pumped so that the urea at least partially from the urea injection valve 54 and urea in the urea line 41 back to the urea tank 40 is rinsed. Step S4 may also be referred to as purge CLEAN.

In a step S5, the program can be ended. Preferably, the program is regularly during operation of the internal combustion engine 14 processed. In addition, if the program when switching off the internal combustion engine 14 is started, in step S15, the pressure in the urea tank 40 be lowered to the ambient pressure.

The invention is not limited to the specified embodiments. For example, the fuel return line 44 thermally with the urea tank 40 be coupled to heat the urea in the urea tank 40 , Furthermore, the urea line 41 with the fuel return line 44 for heating the urea in the urea line 41 be coupled. Furthermore, the urea metering system can also without the pressure port 60 be educated. Furthermore, the flushing process CLEAN can also be performed independently of the switching off of the internal combustion engine. Furthermore, at an overload of the air compressor 50 the air compressor 50 be switched off for a predetermined period of time. The urea tank 40 then serves as accumulator.

Claims (7)

Urea metering system for an internal combustion engine ( 14 ), the at least one cylinder (Z1) with a combustion chamber ( 9 ) and an exhaust tract ( 4 ), which depends on a switching position of a gas outlet valve ( 13 ) with the combustion chamber ( 9 ), wherein the urea-metering system - a urea injection valve ( 54 ) for metering urea into the exhaust gas tract ( 4 ), - a urea tank ( 40 ), from which via a urea line ( 41 ) Urea to the urea injection valve ( 54 ), - an air compressor ( 50 ), which is so with the urea tank ( 40 ) is coupled with the air compressor ( 50 ) an overpressure in the urea tank ( 40 ) can be generated. Urea metering system according to claim 1, comprising a venting line ( 56 ), which is used to purge the urea line ( 41 ) with the air compressor ( 50 ) and the urea injection valve ( 54 ) is coupled. Urea metering system according to one of the preceding claims, which for connecting an external compressed air line, a compressed air connection ( 60 ) associated with the air compressor ( 50 ) is coupled. Method for metering urea by means of the urea metering system according to one of the preceding claims, in which an overpressure in the urea tank ( 40 ) is produced and in which the urea by means of the pressure in the urea tank ( 40 ) to the urea injection valve ( 54 ). Method according to Claim 4, in which the urea injection valve ( 54 ) via the vent line ( 56 ) is pressurized so that the urea through the urea line ( 41 ) back to the urea tank ( 40 ) is rinsed. Method according to Claim 5, in which the urea injection valve ( 54 ) via the vent line ( 56 ) is pressurized so that the urea through the urea line ( 41 ) back to the urea tank ( 40 ) is flushed when the internal combustion engine ( 14 ) is switched off. Device for metering urea by means of the urea metering system according to one of claims 1 to 3, which is designed to be in the urea tank ( 40 ) to generate an overpressure and the urea by means of the positive pressure to the urea injection valve ( 54 ).