Damping element and arrangement for dosing a liquid with a damping element

Abstract

Damping element (11, 111, 211) for hydraulic and / or pneumatic damping of pressure fluctuations in a fluid-carrying arrangement (1), comprising a body (26, 28; 26, 50) having a cavity (22), wherein the cavity (22) can be pressurized with a fluid pressure, and wherein at least one wall section (21, 210) of the wall of the cavity can yield elastically under the fluid pressure, wherein the wall section (21, 210) is configured such that it comes into contact with the fluid on the side facing the cavity and is pressurized with the ambient air pressure (38) on the side facing away from the cavity, characterized in that the wall section (21, 210) has a compensating element (24, 240) and a support element (28, 280), wherein the support element (28, 280) supports the compensating element (24, 240) at several locations (25, 36) distributed over the surface of the leveling element (24, 240) bears at least when the leveling element (24,240) has undergone a predetermined maximum deformation due to an application of fluid pressure, wherein the support element (280) always supports the compensating element (240) at several points (25) distributed over the surface of the compensating element (240), i.e., regardless of an application of fluid pressure, and wherein the compensating element (240) is formed by several fluid-tight elastomer windows which are held by the support element (280).

Description

Prior ArtThe invention is based on a damping element or an arrangement for metering a liquid according to the species of the independent claims. In motor vehicles which are driven by an internal combustion engine, the nitrogen oxides which are produced during operation of the internal combustion engine must be reduced, among other things, because of more stringent exhaust gas regulations. A known method for this is the method of selective catalytic reduction, in which the nitrogen oxides are converted into nitrogen and water, in particular with the aid of a liquid reducing agent. In this case, it is known from EP 2 094 954 A1 to convey the reducing agent from the tank to a metering module in a long line via a feed pump close to the tank. The metering module has, for example, an electric valve, via which the required quantity of reducing agent can be metered to the exhaust tract in an electrically controllable manner.DE 199 47 198 A1 describes the use of a pulsation damper in the context of a device for aftertreating exhaust gases of an internal combustion engine. If a piston pump is used as a feed pump, this leads to pressure surges in the hydraulic circuit, as a result of which the operation of a pump suction valve and a pump pressure valve can be disturbed. The result is a reduced pump output or an erroneous metering by the metering module. This phenomenon is counteracted in DE 199 47 198 A1 with a hydraulic damping element or a pulsation damper.A device for preventing or reducing pressure impacts in line networks is also already known from DE 19 63 709 A.DE 100 61 188 A1 discloses a pulsation damper for damping pressure fluctuations of an oscillating positive displacement pump connected thereto. Within damping chambers of the pulsation damper, damping elements made of spring-elastic material are used. The damping elements are located in a region separated from the rest of the damping chamber by a separating membrane within the respective damping chamber. The remaining region of the damping chamber above the separating membrane is the region carrying the conveying medium. In this case, the separating membrane can be arranged such that it is exposed in the unloaded state, that is to say is spaced apart from the damping material by an air gap which is separated from the ambient air. The separating membrane thus acts as a spring element which dampens small pressure peaks. Only when higher pressures are applied is the separating membrane deformed to such an extent that it can rest on the damping elements and be elastically supported by them.DE 72 06 724 U describes a pulsation damper for hydraulic systems having a pressure vessel connected to a pressure line, wherein the pressure vessel has at least one wall section which is bounded by a buckling edge of the pressure vessel wall and which is elastically stressed in bending by the pulsating pressure fluctuations of the pressure medium. Devices for damping pressure pulsations in a fluid system, in particular in a fuel system of an internal combustion engine, or pressure peak suppressors, are also known from DE 103 27 408 A1 and DE 37 24 381 A1.Disclosure of the InventionThe damping element according to the invention or the arrangement according to the invention for metering a liquid having the characterizing features of the independent claims have the advantage over the related art that a damping function or a pressure-fluctuation-damped metering function can be provided in a simple and temperature-independent manner. In this case, volume expansions arising as a result of the freezing of a liquid provided for metering are also advantageously easily absorbed, as a result of which a cryoprotective means is simultaneously provided. According to the invention, on the one hand, an elasticity for compensating fluid pressure fluctuations even at low temperatures or for compensating an ice pressure is ensured and, on the other hand, independently thereof, a sufficient rigidity for recovering the initial shape of a compensating element even at high temperatures is ensured.By means of the measures specified in the dependent claims and in the description, advantageous refinements and improvements of the damping element specified in the independent claims or of the specified arrangement for metering are possible.Brief Description of the DrawingsExemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. They show FIG. 1 shows a metering arrangement, FIG. 2 shows a damping element, and FIG. 3 shows a further damping element.Embodiments of the InventionFIG. 1 describes a dosing arrangement 1 for the post-engine dosing of an aqueous urea solution into an exhaust tract of an internal combustion engine, not shown in detail, via a dosing module 13 designed, for example, as an actively switchable valve. A connecting line 15 branches off from the pressure line, which connects a damping element 11 to the pressure line.The damping element 11 can be filled with the aqueous urea solution as a result of the fluidic connection to the pressure line and thus damp pressure fluctuations which occur in particular in the pressure line, for example as a result of the piston stroke activity of the feed pump.FIG. 2 shows a damping element 111, which has a housing 26. The housing 26 has an opening 20, via which the interior 22 of the housing can be filled or acted upon with a fluid, in particular a fluid subject to pressure surges. On the side opposite the opening 20, that is to say in the wall section 21, the housing has a protuberance into the interior space or cavity 22, which protuberance serves as a supporting body 28 for an elastic layer 24. The elastic layer 24 is fastened in a fluid-tight manner on its entire edge region 36 by means of a clamping device 34, so that no fluid can enter the air-filled regions 30 between the elastic layer 24 and the housing 26 or the supporting body 28. The elastic layer is spaced apart from the supporting body, but at least partially spaced apart, without application of fluid pressure-with the exception of the edge region 36. Partially spaced means, for example in the case of a corrugated elastic layer, as depicted in FIG. 2, that this can rest on the supporting body 28 at one or more points 25 even without application of fluid pressure. The support body 28 has openings 32 which allow an air exchange between the ambient air region 38 on the one hand and the variable air cushions 30 located between the support body 28 and the elastic layer 24 on the other hand.The damping element 111 has the elastic layer 24, which is made of an elastomer or rubber material and performs the damping function (elastomer damper). In this case, the elastomer damper 24 is acted upon on one side, that is to say on the side facing the interior 22, with the pulsating liquid, in particular an aqueous urea solution, as explained in connection with the description of FIG. 1, and on the other side with ambient air via the openings 32. Both the elasticity of the rubber material and the throttling effect of the small openings 32 contribute to damping of the fluid pulsations, in particular in a metering arrangement according to FIG. 1 connected to the opening 20. In contrast to DE7206724U, the wall section subjected to flexurally elastic stress is formed by an elastomer damper which is protected from uncontrolled collapsing by means of the supporting body 28 of high rigidity and can be held in an intended shape, in particular for protection from irreversible deformations.In a simpler embodiment, instead of a wavy shape, a flat shape adapted to the contour of the supporting body 28 can also be selected for the elastic layer 24 in such a way that the layer 24 in the unloaded state is arranged substantially continuously spaced apart from the supporting body and rests on the supporting body 28 or the housing 26 only around the edge region 36.FIG. 3 shows a damping element 211 according to the invention, which can likewise be connected to a metering arrangement according to FIG. 1 (at the location of the damping element 11 shown there). The same reference numerals as used in the description of FIG. 2 denote the same or similar components and will not be explained again in more detail. In comparison to the damping element according to FIG. 1, the wall section 21 is replaced by a wall section 210 which is provided by an integrated compensating arrangement 50. This compensating arrangement 50 has a supporting body 280 in the form of a supporting frame or in the form of supporting sections which are not necessarily connected to one another and which are rigid with respect to fluid pressure loads which occur during operation in comparison with the elastomer windows 240 which seal off the supporting frame in a fluid-tight manner and take over the damping function. These elastomer windows can be made of the same material as the supporting frame, but with a smaller wall thickness-in order to ensure an elasticity for damping pressure fluctuations-and / or they can consist of a softer elastomer than the supporting frame.In this damping element, the two functions of elasticity and recovery of the initial shape are separated in design. The rigidity is formed via a skeleton made of plastic, the supporting frame 280. Correspondingly selected plastic, for example PA (polyamide), POM (polyoxymethylene) or PE (polyethylene), is less temperature-sensitive with respect to its rigidity. This plastic skeleton has a plurality of windows which are closed, for example, by a thin-walled and thus elastic elastomer, for example EPDM (ethylene-propylene-diene rubber). The entire skeleton body can thus be encapsulated with a thin elastomer sheath or dipped into a corresponding elastomer bath during the production of the compensating arrangement 50, which must subsequently be connected fluid-tightly to the remaining part of the housing 26 of the damping element 211. Plastic and elastomer adhere very well to one another, so that a compact unit and no relative movement between elastomer and plastic is produced, thus ensuring good durability.By shaping the skeleton or supporting body 280, a corresponding stiffness or deformability of the damper can be represented. Thus, the windows in the support body can be arranged in an alternative embodiment, for example in a worm shape. In this case, the plastic skeleton functions as a cylindrical compression spring.By providing a rigid supporting frame with integrated elastic windows, firstly a temperature-independent rigidity of the compensating arrangement is ensured via the supporting frame and secondly a pressure-fluctuation-damping elasticity is ensured via the elastic windows even at low temperatures. In this case, the two functions of temperature-independent stiffness on the one hand and elasticity on the other hand can be optimized next to one another. This solves the problem that otherwise, in particular at low temperatures, an elastomer may under certain circumstances become very stiff and lose its damping effect. If, on the other hand, attempts were made solely by reducing the wall thickness or by a soft rubber mixture to represent the elasticity required at low temperatures, then the recovery of the starting form would be critical at high temperatures. As described, the invention solves this problem by materially separating the elasticity and recovery functions of the initial shape.

Claims

Damping element (11, 111, 211) for hydraulically and / or pneumatically damping pressure fluctuations in a fluid-carrying arrangement (1), having a body (26, 28; 26, 50) which has a cavity (22), it being possible for a fluid pressure to be applied to the cavity (22), and it being possible for at least one wall section (21, 210) to elastically flex under the fluid pressure to the wall of the cavity, the wall section (21, 210) being designed such that it comes into contact with the fluid on the side facing the cavity and is subjected to the pressure of the ambient air (38) on the side facing away from the cavity, characterized in that the wall section (21, 210) has a compensating element (24, 240) and a supporting element (28, 280), the supporting element (28, 280) having the compensating element (24, 240) at a plurality of points (25, 25 distributed over the surface of the compensating element (24, 240), 36) carries at least when the compensating element (24, 240) has undergone a predetermined maximum deformation due to an application of the fluid pressure, wherein the support element (280) carries the compensating element (240) always, i.e. independently of an application of the fluid pressure, at a plurality of points (25) distributed over the surface of the compensating element (240), and wherein the compensating element (240) is formed by a plurality of fluid-tight elastomer windows which are held by the support element (280).Damping element according to Claim 1, characterized in that the supporting element (280) is formed by a single-part or multi-part rigid supporting frame.Damping element according to Claim 2, characterized in that the elastomer windows are bounded by the supporting framework.Damping element according to Claim 2 or 3, characterized in that the elastomer windows and the supporting framework are arranged in the form of a worm, with the result that the compensating arrangement (50) formed by the supporting element (280) and the compensating element (240) can operate like a cylindrical compression spring under fluidic loading.Arrangement (1) for metering a liquid, which arrangement has a feed pump (7) for drawing in a liquid from a tank, wherein the feed pump (7) is connected via a pressure line (9) to a metering module (13), characterized bya damping element (11, 111, 211) according to one of the preceding claims, which damping element is connected to the pressure line (9).Arrangement according to Claim 5, characterized in that the feed pump is a piston pump.Arrangement according to Claim 5 or 6, characterized in that it is designed to meter a reducing agent into the exhaust tract of an internal combustion engine in order to reduce pollutants contained in the exhaust gas of the internal combustion engine.

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