DE102007027413B4 - Reducing agent supply system for an exhaust gas purification catalyst of an internal combustion engine - Google Patents

Abstract

Reducing agent supply system for an exhaust gas purification catalyst (1) of an internal combustion engine, in particular of a motor vehicle,
with a reducing agent tank (3) for receiving liquid reducing agent,
an electrically heatable liquid line (6, 7) for conveying reducing agent from the reducing agent tank (3) to an exhaust gas purifying catalyst (1),
and a pump (5) for pumping reducing agent through the liquid line (6) from the reducing agent tank (3) to the exhaust gas purifying catalyst (1),
wherein at least a portion of the liquid conduit (6, 7) is formed as a metal pipe contacted with electrical terminals for conducting an electric heating current through the metal pipe for heating the liquid conduit (6, 7), and
characterized in that the metal tube (6, 7) consists of an alloy which is pseudoelastic at least at the freezing point of the reducing agent.

Description

The invention is based on a reducing agent supply system for an exhaust gas purification catalyst, as is known from the WO 2006/136306 is known. Such a reductant supply system includes a reductant tank, an electrically heatable fluid line, and a pump to pump reductant through the fluid line from the reductant tank to the catalyst.

The term exhaust gas purifying catalyst is used in the context of the application in accordance with the customary in vehicle technology language for a device for exhaust gas purification, which may contain a catalyst in the chemical sense. Such exhaust gas purification catalysts are installed as standard in motor vehicles. In general, the reducing agent is added to an exhaust gas stream before it reaches the region of the exhaust gas purification catalyst containing the catalyst in the chemical sense.

With the reducing agent, nitrogen oxides in the exhaust gas purifying catalyst are reduced to nitrogen. As a reducing agent in the true sense of ammonia is used by default, which is obtained from urea. For the purposes of the application, a reducing agent is therefore also understood to mean its precursor, for example urea, from which the actual reducing agent in the chemical sense, for example ammonia, is obtained, and a solution, in particular aqueous, prepared therewith.

In the case of frost, the urea solution, which is required as an ammonia supplier by an exhaust-gas purification catalyst, can freeze. For this reason, electrically heated liquid lines are used for reducing agent supply systems, so that urea solution can be pumped rapidly to the catalyst even in heavy frost.

In the from the WO 2006/136306 known reducing agent supply system thin stainless steel tubes are used as liquid lines through which an electric current is passed for heating. In the known system thin stainless steel tubes with an inner diameter of less than 4 mm and a wall thickness of 0.2 mm to 0.3 mm are used as liquid lines and at the same time as resistance heating elements. This is possible because such stainless steel tubes have a sufficiently high electrical resistance to cause a heating power when applying the usual on-board voltage of a motor vehicle, which is well suited for thawing contained in the tubes urea solution.

Upon freezing, urea solution expands by more than 7% by volume under atmospheric pressure and can produce greater ice pressure than water of many hundreds of bars. So that the pipes of a urea supply system are not damaged by such a volume expansion, it is from the WO 2006/136306 known to insert in the lines an elastic volume compensation element, such as a plastic strand with gas-filled chambers. The volume compensation element is compressed when freezing surrounding urea solution and can thus compensate for the volume expansion of the urea solution. However, the chambers of such a volume compensating element may outgas with time so that they collapse and the compressibility of the volume compensating element fades.

To protect the fluid lines of a urea supply system against frost damage, it is from the WO 2006/136306 Also known to use stainless steel tubes with a deviating from the circular cross section, for example, with an elliptical cross section. A volume expansion of the urea solution occurring during freezing causes the tube cross section to approach or even reach the circular shape. In this way, the cross-sectional area of the metal tube and thus its internal volume can adapt to frost, so that a bursting of the line is prevented. After thawing, however, a stainless steel tube largely retains its now circular cross-section, so that in this way only a one-time protection against forest damage can be achieved.

To avoid frost damage, it is also known to automatically empty the lines of the urea supply system of a motor vehicle when switching off the engine or to use elastic plastic hoses instead of bursting endangered stainless steel pipes. The disadvantage of this, however, is that in case of failure of the pump urea solution remains in the lines and then cause damage in frost. In addition, a complete emptying of the lines usually does not succeed and remain droplets. These droplets can evaporate, precipitating urea crystals, which dissolve in the concentrated urea solution only poorly and can clog the line. Although plastic hoses are frost-proof, they can be damaged relatively easily, for example by rodents.

The object of the invention is to show a reliable way how a frost-proof reducing agent supply system for a motor vehicle can be created.

This object is achieved by a reducing agent supply system with the in claim 1 specified characteristics solved. Advantageous developments of the invention are the subject of the dependent claims.

According to the invention, a metal tube made of an alloy which is pseudoelastic at least at the freezing point of the liquid reducing agent is used as the liquid line. Such alloys may be either austenitic or martensitic, depending on the temperature selected. Martensite is at the lower temperature, austenite at the higher temperature. The temperature at which the alloy begins to convert from austenite to martensite upon cooling is called the transition temperature or the Ms point.

If the Ms point is not reached, the transformation of austenite into martensite does not take place abruptly; rather, the transformation takes place over a temperature range; the transformation of austenite into martensite and martensite into austenite shows a hysteresis. Below the Ms point, such alloys can exhibit shape memory in the martensitic state: A plastic deformation in the martensitic state can be reversed by heating to temperatures above the Ms point. In the austenitic state, such a shape memory alloy can exhibit pseudoelastic behavior. The larger the ratio of austenite to martensite, the more pronounced the pseudoelastic behavior is. The pseudoelastic behavior is characterized by the fact that the force requirement for increasing elongation, while initially appreciable, as with an austenite, increases significantly, but only increases slightly after reaching about 1% to 2% elongation with further expansion, and only after reaching larger strains of 6% to 8% rises steeply again. The mean strain range is referred to as the "martensite plateau". The name comes from the fact that martensite forms in the alloy under the influence of tensile stress. If the material is relieved by the train, it returns to the austenitic state. These pseudoelastic strains are highly reversible, up to strains greater than 6% to 8%.

Therefore, a metal tube of a pseudoelastic alloy can withstand an expansion forced by freezing urea solution, and in a subsequent thawing of the solution, its cross-sectional area is reduced again, so that a large number of freezing and thawing cycles can be overcome without damage.

Preferably, the pseudoelastic alloy is a nickel-titanium alloy, for example an alloy known under the trade name Nitinol, which contains nickel and titanium in approximately equal atomic percentages. Pseudoelastic nickel and titanium alloys are chemically very resistant to corrosion and can resist a urea solution over a period of many years.

Preferably, the shape memory alloy has a transition temperature (Ms point) which is below the freezing point of the solutions used in the reducing agent supply system, in particular urea solution. This measure has the advantage that the pseudoelastic alloy is always present during freezing of the solution in its high-temperature phase, which is important for the pseudoelastic behavior.

The usual for motor vehicles aqueous urea solution has a freezing point of -11 ° C. The pseudoelastic alloy is therefore selected to have a temperature range in which it transforms from austenite to martensite, which is the freezing point of the urea solution of e.g. B. -11 ° C or preferably lies below. Preferably, the transition temperature is below -11 ° C, preferably below -20 ° C or even below -40 ° C, so that the pseudoelasticity of the alloy even in heavy frost can compensate for the increase in volume of the freezing aqueous reducing agent reversible.

Further details and advantages of the invention will be explained by means of embodiments with reference to the accompanying drawings. In this case explained features can be made individually or in combination to the subject of claims. Identical and corresponding components are identified in the figures with corresponding reference numerals. Show it:

1 a schematic representation of an embodiment of a urea supply system for an exhaust gas purification catalyst of a motor vehicle; and

2 an embodiment of a connector that connects two liquid line sections of the reducing agent supply system.

1 schematically shows an exhaust gas purification catalyst 1 a motor vehicle and an associated reductant supply system 2 , which works in particular with a urea solution. In the exhaust purification catalyst 1 Nitrogen oxides are reduced to nitrogen by means of ammonia. The ammonia required for this purpose is obtained from the urea solution supplied by the reducing agent supply system 2 provided and in the catalyst 1 the exhaust gas flow 1b via a metering valve 1c is added.

This in 1 shown reducing agent supply system 2 includes a reducing agent tank 3 for receiving a urea solution 4 as a reducing agent, an electrically heated liquid line 6 to the reducing agent from the reducing agent tank 3 to the exhaust gas purifying catalyst 1 to transport a pump 5 to the reducing agent through the fluid lines 6 from the reducing agent tank 3 to the catalyst 1 to pump, and a heating insert 8th for heating the urea solution in the tank 3 , From the liquid line 6 branches in the flow direction behind the pump 5 a return line 7 off, in the tank 3 leads, so that heated urea solution into the tank 3 can be returned.

The pump 5 and the catalyst 1 be from a control unit 11 controlled, the frost in an electrical heating of the reducing agent tank 3 , the pump 5 , the lead 6 and preferably also the return line 7 turns. The control unit may be the engine control of the vehicle, which receives data about the outside temperature via sensors and can therefore determine the need for heating. Temperature sensors may also be on or in portions of the reductant delivery system 2 be provided, for example, in or on the tank 3 or the pump 5 ,

At least the line 6 , preferably also the line 7 , is formed of one or more metal pipes of a pseudoelastic alloy, preferably a nickel-titanium alloy, which is contacted with electrical terminals for heating the liquid pipes 6 . 7 to pass an electric heating current through the metal pipes. To heat between the ends of the lines 6 . 7 forming an electric voltage forming metal tubes so that a current flows. The metal pipes 6 . 7 are heated by the current flowing through them and thus used as a kind of resistance heating elements. The wires 6 . 7 forming metal pipes preferably have a total length of at least 3 m, typically 3.5 m to 9 m. In this case, individual metal tubes can be assembled one behind the other or uninterrupted continuous tubes of appropriate length can be used. The wires 6 . 7 Preferably, however, contain at least one metal tube with a length of at least 1 m, preferably at least 2 m, in order to keep the number of pipe joints as small as possible.

Freezed in the metal pipes 6 . 7 Urea solution, its volume increases by about 7%. This increase in volume leads to an elongation of the metal tubes 6 . 7 , which survive without damage because of their pseudoelastic properties and reversibly return to their original shape in a subsequent thawing of the urea solution. Commercially available pseudoelastic nickel-titanium alloys, which are sold, for example, under the trade names Nitinol or Flexinol, have an elastic limit of more than 8% owing to their pseudoelastic properties and can therefore be stretched reversibly by up to 8%.

Such pseudoelastic alloys can be produced at different transformation temperatures. Conveniently, the shape memory alloy used has a transition temperature of below 0 ° C, preferably below -11 ° C, for example -50 ° C, so that the pseudoelastic properties of the alloy can be used in freezing the urea solution to compensate for the volume increase occurring during freezing.

With frequent deformation, pseudoelastic alloys can exhibit signs of fatigue leading to reduced pseudoelasticity. It is therefore advantageous if the metal tubes 6 . 7 have a shape deviating from the cylindrical shape, for example, are shaped as a corrugated tube or have a deviating from the circular shape, for example, have an elliptical or kidney-shaped cross-section. In this way, with a freezing of urea solution, the necessary increase in the internal volume of the metal tubes 6 . 7 even at a lower strain than in cylindrical tubes can be achieved.

The of the metal pipes 6 . 7 flow-through cross-sectional area trapped at room temperature, that is to say the clear internal cross-sectional area, is less than 20 mm ² , preferably less than 17 mm ² , in the illustrated exemplary embodiment. The wall thickness is advantageously 0.1 mm to 1 mm, preferably 0.2 mm to 0.8 mm, in the illustrated embodiment, 0.6 mm. Supplementary should be in the design of the metal pipes 6 . 7 It should be noted that for the heating of the reducing agent supply system in a car typically a heating power of not more than 100 watts is available, which is applied by the vehicle battery.

The metal pipes 6 . 7 are with connectors to other parts of the reductant supply system 2 , for example to the pump 5 and to the metering valve 1c connected. An embodiment of a suitable connector is in 2 shown.

The connector comprises a coupling 24 as a female connector, the openings for receiving plugs 13 . 14 . 15 has as male connecting parts. The one of a metal tube of the liquid line 6 worn at its two ends plug 13 is from an insulator 16 and one surrounding him metal sleeve 17 , preferably made of stainless steel, formed. In the illustrated embodiment, the insulator 16 a plastic body that holds the metal tube 6 encloses and from the metal sleeve 17 is enclosed. The metal sleeve 17 electrically contacts the end of the metal tube with its end 6 by being materially bonded to it. In the embodiment shown, the metal sleeve 17 with the edge of the metal tube 6 welded, so that the metal sleeve 17 and the metal tube 6 just touch at their ends.

The metal sleeve 17 touched in the clutch 24 an electrical contact 18 , which is preferably designed as a detent spring. The electrical contact 18 is connected to an electrical line 19 connected, over which in operation the heating current through the metal sleeve 17 to the metal pipe 6 flows. In this way, the metal tube 6 Traversed by the heating current and heated over its entire length.

The metal sleeve 17 is in the illustrated embodiment form-fitting with the plastic body 16 connected. In this way, a displacement of the sleeve 17 relative to the plastic body 16 prevented. In the illustrated embodiment, the positive connection of openings of the sleeve 17 caused by the locking lugs 21 of the plastic body 16 reach through. At its rear end is the metal sleeve 17 slotted. This measure has the advantage that the metal sleeve 17 when pushed onto the plastic body 16 something spreads, leaving the plug 13 easier to assemble.

Seals designed as O-rings 20 prevent leakage of fluid between the plugs 13 . 14 . 15 and the clutch 24 , The plug 13 has at its rear end a pocket for receiving an insulation cover 22 of the metal pipe 6 ,

The one in the clutch 24 plug-in plug 15 is a standard connector, such as the pump 5 , the tank 3 or the metering valve 1c can be appropriate. Such a standard plug 15 is usually not heated. In the illustrated embodiment, therefore, protrudes into the plug 15 a heating rod 23 into it. The heating rod 23 is from an electrical connector 14 carried in the third opening of the clutch 10 plugged. The heating rod 23 is just like the metal tube 6 over a metal sleeve 17 and an electrical contact 18 to the line 19 connected.

In the embodiment shown, the inner diameter of the liquid channel in the standard plug 15 for simplicity, as large as the inner diameter of the metal tube 6 shown. Conveniently, the inner diameter of the metal tube 6 but smaller than the inner diameter of the liquid passage in the standard plug 15 ,

According to 1 , is at the heating insert 8th on to the liquid line 6 connected intake pipe 9 attached to aspirate urea solution. The output of the return line 7 is designed and arranged such that in operation from the return line 7 exiting urea solution on the intake pipe 9 runs down. In this way, the intake pipe 9 additionally heated. Further, at low tank level, the heating power of the then lying in air intake pipe 9 taken up by the solution running down it and fed to the liquid circulation.

In the illustrated embodiment, the heater is 8th in a thawing container 10 arranged, both to the return line 7 as well as to the liquid line 6 connected and in the illustrated embodiment in the reducing agent tank 3 is arranged. The defrost container 9 causes the heating power of the heating insert 8th initially primarily for heating the in the thawing container 9 contained urea solution can be used.

About the intake pipe 9 can both from the thawing container 10 as well as from the rest of the tank 3 Urea solution be sucked. Namely, the intake pipe protrudes through the thawing container 10 into the tank 3 into it, so that through a suction opening from the thawing container 10 and through a second suction port from the tank 3 Urea solution can be aspirated. The defrost container 10 has an overflow opening, not shown, so that when sucking urea solution through the second intake through the return line 7 improved heat distribution can also be used for thawing the remaining urea solution, which is outside the thawing container 10 located.

At the intake pipe 9 is a highly thermally conductive, elastic plastic pipe, for example, EPDM with a Shore hardness of 60 to 80 Shore A. The intake manifold 9 carries two electrical connection lines (not shown), which come from the housing of the heating element 8th go out and provide the at least one heating element arranged therein with electricity. In principle, a single electrical connection line would be sufficient if a ground contact to the at least one heating element is produced in another way. The connecting cables have a plastic sheath that encloses a metal wire or a stranded wire.

During operation, heating of the connecting cables takes place through ohmic resistance heating. The heat emitted by the connection lines heat is delivered to the carrying connection pipe and its immediate environment, so that the ice contained therein thawed quickly and a gap, can be done on the suction of liquid pressure equalization, can be melted free. The flexible intake pipe 9 extends in the thawing container 10 starting from the housing of the heating insert 8th self-supporting up to the liquid line 6 to which it is connected.

While metal pipes because of their high reliability and good heatability outside the tank 3 are beneficial, is in the tank 3 a flexible intake pipe 9 is preferred because when freezing surrounding urea solution bending moments can occur, resulting in damage to a metal pipe with those for the liquid line 6 suitable dimensions could lead to which the flexible intake manifold 10 but can yield without harm.

LIST OF REFERENCE NUMBERS

1

purifying catalyst

1b

exhaust gas flow

1c

metering valve

2

Reducing agent supply system

3

Reductant tank

4

urea solution

5

pump

6

Liquid line, metal tube

7

Return line, metal tube

8th

heater

9

intake

10

defrosting

11

control unit

12

switch

13

plug

14

plug

15

plug

16

insulator

17

metal sleeve

18

Contact

19

management

20

O-ring

21

locking lugs

22

insulating sleeve

23

heater

24

clutch

Claims (15)

Reducing agent supply system for an exhaust gas purifying catalyst ( 1 ) of an internal combustion engine, in particular of a motor vehicle, with a reducing agent tank ( 3 ) for receiving liquid reducing agent, with an electrically heatable liquid line ( 6 . 7 ) to remove reducing agent from the reducing agent tank ( 3 ) to an exhaust gas purifying catalyst ( 1 ) and with a pump ( 5 ) to reductant through the liquid line ( 6 ) from the reducing agent tank ( 3 ) to the exhaust gas purification catalyst ( 1 ), wherein at least a portion of the liquid line ( 6 . 7 ) is formed as a metal tube, which is contacted with electrical terminals in order to heat the liquid line ( 6 . 7 ) to conduct an electric heating current through the metal tube, and characterized in that the metal tube ( 6 . 7 ) consists of an alloy which is pseudoelastic at least at the freezing point of the reducing agent. Reducing agent supply system according to claim 1, characterized in that the pseudoelastic alloy consists of nickel-titanium, copper-zinc, copper-zinc-aluminum, copper-aluminum-nickel or iron-nickel-aluminum, with a nickel-titanium alloy being particularly preferred is. Reducing agent supply system according to one of the preceding claims, characterized in that the pseudoelastic alloy has a transition temperature of below 0 ° C. Reducing agent supply system according to claim 3, characterized in that the pseudoelastic alloy has a transition temperature of below -11 ° C. Reducing agent supply system according to claim 3, characterized in that the pseudoelastic alloy has a transition temperature of below -20 ° C. Reducing agent supply system according to claim 3, characterized in that the pseudoelastic alloy has a transition temperature of less than -40 ° C. Reducing agent supply system according to one of the preceding claims, characterized in that the metal tube ( 6 . 7 ) has a wall thickness of 0.1 mm to 1 mm. Reducing agent supply system according to claim 7, characterized in that the metal tube ( 6 . 7 ) has a wall thickness of 0.2 mm to 0.8 mm, in particular of 0.6 mm. Reducing agent supply system according to one of the preceding claims, characterized in that the metal tube encloses a flow-through cross-section of less than 30 mm ² , preferably less than 25 mm ² , in particular less than 20 mm ² . Reducing agent supply system according to one of the preceding claims, characterized characterized in that the metal tube ( 6 . 7 ) has a different shape from the cylindrical shape. Reducing agent supply system according to claim 10, characterized in that the metal tube ( 6 . 7 ) in cross-section elliptical, oval or kidney-shaped. Reducing agent supply system according to claim 10, characterized in that the metal tube ( 6 . 7 ) is a corrugated tube. Reducing agent supply system according to one of the preceding claims, characterized in that the metal tube ( 6 ) has an electrical resistance of 0.1 ohms to 0.5 ohms per meter. Reducing agent supply system according to one of the preceding claims, characterized in that the dimensions of the metal tube ( 6 . 7 ) are matched to the existing in the vehicle, especially in cars, electric battery that the metal tube ( 6 . 7 ) is heated when connected to the battery with a power of 5 to 25 watts / m, in particular with 15 watts / m. Reducing agent supply system according to one of the preceding claims, characterized in that the pseudoelastic alloy is selected from the group of shape memory alloys.

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