DE102017218418A1 - Tank, arrangement for the aftertreatment of the exhaust gas of an internal combustion engine with such a tank and operating method - Google Patents

Abstract

Tank (44) for a fluid for aftertreatment of the exhaust gas of an internal combustion engine, in particular for a liquid, preferably an aqueous urea solution, characterized in that it is designed to be positive and / or negative pressure and interacts with a device (32) for pressurizing. Furthermore, an arrangement (44, 111, 25) for the exhaust aftertreatment with such a tank (44) is proposed and a method for operating such an arrangement.

Description

State of the art

The invention relates to a tank for a fluid for the aftertreatment of the exhaust gas of an internal combustion engine and an arrangement for the aftertreatment of the exhaust gas of an internal combustion engine with such a tank. Furthermore, the invention is based on a method for operating such an arrangement.

Due to legal requirements, the exhaust of motor vehicles must comply with certain limits. In order to meet these limit values, exhaust gas aftertreatment arrangements are used downstream of the internal combustion engine, the aim of which is to reduce the particle or nitrogen oxide concentration in the exhaust gas. The filters and catalysts used for this purpose require that certain oxidizing or reducing agents be introduced into the exhaust gas line. For example, an exhaust aftertreatment arrangement is known in which an aqueous urea solution is injected into the exhaust tract upstream of a catalyst for the selective reduction of nitrogen oxides. The urea solution used as reducing agent is conveyed here by means of a delivery module from a tank to a metering module, which delivers the necessary flow rate of the urea solution as a spray into the exhaust gas line.

From the EP0839264 It is already known, lines of an arrangement for the aftertreatment of exhaust gases, which lead aqueous urea solution to the exhaust gas tract of an internal combustion engine, to pressurize a compressed gas, in particular compressed air, in order to empty them.

Disclosure of the invention

The tank according to the invention or the inventive arrangement for exhaust aftertreatment or the inventive method with the characterizing features of the independent claims have the advantage of ensuring sufficient capacity even under marginal operating conditions. Thus, wide ranges of dosing requirements can be covered under all operating conditions without having to exceed the physical performance limits of even heavy hydraulic pumps. Factors which can be overcome by means of the invention are in this case e.g. the height difference between the hydraulic pump and the tank, pressure drops in filters, the strong pressure at high travel heights ambient pressure and the vapor pressure of the stored fluid at a certain temperature, in particular an aqueous urea solution. Thus, a local steam pressure undershooting and thus the occurrence of cavitation and delivery loss of a conveyor module can be effectively countered.

In addition, can be dispensed either advantageously for the purpose of emptying at least parts of the arrangement of the fluid to a reversing valve or a 4/2-way valve.

The over- and / or vacuum-proof tank in combination with a device for pressurizing the tank advantageously allows both a support of a hydraulically operating delivery module and an emptying, be it in the form of a back suction or in the form of a blow-out.

The measures listed in the dependent claims advantageous refinements and improvements of the independent claims specified tanks, the arrangement indicated for the aftertreatment of an exhaust gas and the specified operating method are possible.

list of figures

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1 eine Anordnung mit einem Umschaltventil bzw. 4/2-Wege-Ventil und
• 2 eine Anordnung mit Luftpumpe.

Show it

• 1 an arrangement with a switching valve or 4/2-way valve and
• 2 an arrangement with air pump.

Embodiments of the invention

1 shows a conveyor module 1 to promote an aqueous urea solution 2 from a tank 4 to a dosing or injector 25 , This leads a suction line 17 via a delivery module inlet 16 and via a 4/2 valve or diverter valve 9 to a flow-through pulsation damper or damping element 7 and subsequently to a diaphragm pump 3 with its upstream check valve assembly 5 , Pressure side of the diaphragm pump performs a pressure line 19 via a main filter 11 to the delivery module outlet 20 , wherein the Fördermodulauslaß upstream of a pressure sensor 13 located. Between the main filter 11 and the pressure sensor 13 branches a return line 21 which returns to the tank and which still throttles in the area of the delivery module ( 23 ). In particular in the area of the delivery module inlet 16 , the conveyor module outlet 20 and the tank-side end of the suction line 17 are more filters 15 for filtering the pumped aqueous urea solution 2 built-in.

The damping element 7 in the form of a suction side of the pump 3 arranged pulsation serves to attenuate pressure fluctuations that may arise due to the operation of the pump, and to avoid cavitation.

The throttle 23 can be supplemented or replaced by a check valve and / or a switching valve. Or the throttle 23 is formed by a check valve or a switching valve, which even in the open state throttling acts on a flowing back into the tank backflow.

The fact that an aqueous urea solution can freeze and thereby cause ice pressure damage is in the described construction after 1 by the provision of a Rücksaugmodus the delivery module, ie the suction of aqueous urea solution from the dosing back out into the tank. This is done in a conventional manner using a complex 4/2-way valve, the pumping direction is reversed to suck back by pressing the 4/2-way valve.

2 shows a modified conveyor module 111 , in contrast to the delivery module 1 according to 1 no changeover valve or 4/2-way valve 9 is provided, and instead of a throttle function 23 in the return path as a basic equipment is necessarily at this point a valve 33 provided, either a check valve or an electrically controllable switching valve.

Other same or similar components as in 1 are shown in 2 provided with the same reference numerals and will not be described again.

Further shows 2 instead of the tank 4 according to the arrangement 1 a tank 44 in the case of the use of a check valve in the delivery module at least overpressure-proof or in the case of using an electrically controllable switching valve is designed at least negative pressure. The tank is filled in a known manner with aqueous urea solution, and above the liquid level is air 30 in the tank. According to the invention, an air pump can be retrofitted in a modular manner 32 provided, which preferably in the upper region of the tank 44 So on the tank head 46 , particularly preferably in unit with a tank head designed as a tank cap 46 , is mounted. This air pump is preferably designed as a rotary pump, with the possibility of reversing the conveying direction for air, so that the tank contents can be selectively subjected to an overpressure or a negative pressure.

Alternatively, the modular mounted on the tank or modular retrofit air pump 32 be replaced by an air pump that is not part of the tank head 46 Tank cap is, but mounted separately on the vehicle and with a hose to the tank, preferably with the tank head 46 , connected is.

In the 2 illustrated arrangement for exhaust aftertreatment with tank, delivery module and metering module can be operated as follows:

Is the system in dosing mode for dosing aqueous urea solution via the dosing module? 25 in the not shown exhaust system of an internal combustion engine upstream of a catalyst for selective catalytic reduction promotes the air pump 32 Ambient air in the tank 44 , The pressure in the tank increases as a result, which is why the tank wall must be designed to be stable. For example, the pressure in the tank is higher than the pressure in the ambient air. More tank pressure means that the feed pump 3 less power needed for suction. Ideally, the tank pressure is so high that aqueous urea solution enters the pump chamber of the HWL reciprocating / diaphragm pump by itself 3 flows when it is in the intake stroke. Thus, in the intake stroke no actual intake more. The pump 3 allowed by the retraction / retraction of the pump diaphragm, the inflow of the operating medium. The tank pressure is set at least so high that the influences of low ambient pressure, high temperatures, filter pressure losses and large height differences between tank and HWL pump 3 be compensated, thereby the required system flow rate is always achieved and cavitation events are avoided.

A tank with such an air pump can also be equipped with a delivery module 1 as it is in 1 is shown to be operated when the Rücksaugfunktion continue via a switching valve 9 should or can be provided. If no suck-back function is required, a delivery module can also be used 111 (ie without switching valve), in the embodiment with a check valve at the position 33 ,

If the air pump is also to be used for the purpose of re-sucking, it is at the position 33 in 2 Instead of a purely mechanically acting check valve to provide an electrically controllable switching valve. Typically, there is a difference between the pump 3 and metering valve 25 a system pressure of about 9 bar. The diaphragm pump 3 only serves the dosing, where the switching valve 33 is closed in the return path. If the system is in the suck-back mode, the diaphragm pump is stopped 3 still and the conveying direction (direction of rotation) of the air pump 32 is reversed. This creates a negative pressure in the tank 44 why it must be designed so that its walls can also absorb forces acting inward. Then be switching valve 33 and metering valve 25 opened, aqueous urea solution is sucked back and in the delivery module 111 replaced by incoming air or exhaust gas. The diaphragm pump itself is not emptied. In this case, it must be designed so that it can withstand ice pressure, eg with the aid of pressure compensation elements.

An alternative possibility of providing for the at least partial emptying of the delivery module by means of the air pump is the use of the air pump for emptying the system. Unless the diaphragm pump 3 in its bottom dead center their inlet and outlet does not seal itself through the membrane or a shutdown of the diaphragm pump is done so that supply and drain hydraulically connected to each other, can at air pressure in the tank 44 , with closed switching valve 33 and with open dosing valve 25 the pump 3 and the metering valve 25 be blown. With opened switching valve 33 can both return line 21 as well as metering valve 25 be blown out by blowing out the aqueous urea solution via the metering valve, if the diaphragm pump has a shut-off function in the rest position or the opening pressure of their check valves above the pressure loss of the return line including switching valve and filter.

Advantageous when purged by purging is that in addition to the fact that hydraulic system components can be purged so far with ambient air that minor residues of aqueous urea solution can no longer cause ice damage, it also prevents sooty and hot exhaust gas from being drawn into the system.

In all embodiments, the power of the air pump or its speed can optionally be continuously adapted to a required amount of aqueous urea solution to be metered.

Furthermore, as an alternative or in addition, the speed can be modulated in accordance with the frequency of the pressure / suction cycle of the diaphragm pump 3 , Furthermore, as an alternative or in addition thereto, the air pump can each be briefly stopped when the diaphragm pump is in the pressure stroke. As a result, the suction-side check valve closes easier / faster, which in turn increases the pump efficiency. These modulation variants of the air pump or the device for pressurizing concern the pump-specific cyclic operating behavior of the feed pump 3 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0839264 [0003]

Claims (12)

Tank (44) for a fluid for aftertreatment of the exhaust gas of an internal combustion engine, in particular for a liquid, preferably an aqueous urea solution, characterized in that it is designed to be positive and / or negative pressure and interacts with a device (32) for pressurizing. Tank (44) after Claim 1 , characterized in that the device (32) is a device for acting on the tank with a compressed gas, in particular air, preferably ambient air. Tank (44) according to one of the preceding claims, characterized in that the device for pressurizing in the upper region of the tank, in particular a tank head (46), is arranged. Tank (44) after Claim 3 Characterized in that the upper region of the tank has a gas cap, and that the means (32) for pressurizing in the cover (46) is integrated. Tank (44) after Claim 3 or 4 , characterized in that the means (32) for pressurizing forms a direct interface between ambient air and air space (30) in the tank. Tank (44) after one of Claims 1 or 2 , characterized in that the means for pressurizing via a hose through a tank wall or through a lid (46) of the tank through with an air space (30) of the tank is in communication. Arrangement (44, 111, 25) for the aftertreatment of the exhaust gas of an internal combustion engine with a tank (44) according to one of the preceding claims, characterized in that a delivery module (1, 111) is provided which delivers the fluid via a suction line (17) suck out the tank (44) and can supply via a pressure line (19) to a metering module (25) which is adapted to inject the fluid into the exhaust gas. Method for operating an arrangement according to Claim 7 , characterized in that in a metering mode for injecting the fluid into the exhaust gas, the tank (44) is pressurized via the means (32) for pressurizing. Method according to Claim 8 , characterized in that in an emptying mode for at least partially emptying the conveyor module (1, 111) and / or the dosing (25), the conveyor module off and the dosing (25) is opened and that the means (32) for pressurizing the tank with Overpressure or negative pressure to blow out the fluid from the metering module (25) or to suck from the metering back into the tank (44). Method according to Claim 8 or 9 , Characterized in that the performance of the device (32) is modulated for pressurization. Method according to Claim 10 , Characterized in that the modulation of the power of the device (32) in the dosing is carried out according to the amount of required fluid. Method according to Claim 10 or 11 , characterized in that the modulation of the power of the device (32) takes place in the metering mode in dependence on the pump-specific cyclic operating behavior of the conveyor module.

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