DE102014207754A1 - Sensor arrangement for measuring pressure in a freeze-prone medium, medium-conducting device with a sensor arrangement, system for metering a reducing agent into an exhaust gas stream of an internal combustion engine and internal combustion engine - Google Patents

Abstract

The invention relates to a sensor arrangement (7) for pressure measurement in a medium susceptible to freezing, comprising a medium-conducting device (5) which has an at least partially flexible wall (11), wherein a pressure sensor (9) extends through a flexible wall region (15) of one medium-conducting device (5) is arranged separately and arranged to measure a pressure in the medium based on a state of the flexible wall region (15).

Description

The invention relates to a sensor arrangement according to claim 1, a medium-conducting device according to claim 6, a system for metering in a reducing agent according to claim 8 and an internal combustion engine according to claim 11.

In the case of medium-conducting devices which carry freeze-risk media, there is always the risk of damage to components by freezing medium. This is especially true for pressure sensors, which are provided for pressure detection in a medium-conducting device of the type mentioned here. If the medium freezes, considerably higher forces act on a pressure sensor than is the case during normal operation of the medium-conducting device. This can damage or even destroy the pressure sensor. This is particularly the case with medium-conducting devices which are provided in systems for metering a reducing agent into an exhaust gas stream of an internal combustion engine. A common reducing agent is, for example, a urea-water solution, which freezes depending on the urea concentration already in the freezing point or at low minus temperatures, for example in the range of -10 ° C. Pressure sensors are typically provided in such systems to check if a fore pump is operating properly and / or to control high pressure downstream of a high pressure pump of the system. With the aid of at least two pressure sensors it is also possible to perform differential pressure measurements for system diagnostics, for example to monitor the degree of soiling of a filter for the reducing agent. These pressure sensors are threatened in a special way by frost damage, in particular, a mechanical destruction of the pressure sensors is possible.

The invention is therefore based on the object to provide a sensor arrangement which avoids the disadvantages mentioned. The invention is also based on the object, a medium-conducting device, a system for metering a reducing agent in an exhaust stream of an internal combustion engine, and to provide an internal combustion engine in which the disadvantages mentioned do not occur.

The object is achieved in which a sensor arrangement with the features of claim 1 is provided. The sensor arrangement is set up for measuring a pressure prevailing in a medium which is at risk of freezing. In this case, a medium-conducting device has an at least partially flexible wall. A pressure sensor is separated by a flexible wall portion of the wall from a medium which flows through the medium-conducting device, and the pressure sensor is arranged to measure a pressure in the medium based on a state of the flexible wall portion. Because the pressure sensor is separated from the freeze-prone medium by the flexible wall area, it is protected from damaging or destructive action of the medium when it freezes. At the same time, the pressure in the medium can be measured in a simple and precise manner on the basis of the state of the flexible wall area. The sensor is therefore protected on the one hand, on the other hand, there is no disadvantage with respect to the pressure measurement in the medium. The region-wise flexible wall is on one side - in the region of an inner side - in contact with the freeze-prone medium, wherein the pressure sensor outside the flexible wall region, that is arranged in the region of an outer side and thus is not in contact with the freeze-prone medium.

Because the wall area is designed to be flexible, it is deflected depending on the pressure in the freeze-prone medium from a non-pressurized, relaxed or preloaded functional position, this deflection can be regarded as a state of the flexible wall area, which is detected directly or indirectly by the pressure sensor.

An embodiment of the sensor arrangement is preferred, which is characterized in that the pressure sensor is arranged in the wall of the medium-conducting device, wherein it is spaced from the flexible wall area by a protective volume. In this case, the pressure sensor is arranged retracted in the wall, wherein between this and the flexible wall portion, the protective volume is arranged. The flexible wall area is deflected by the freezing medium more than at normal operating pressure, in particular, it is deflected into the protective volume into it. The pressure sensor is protected by its retracted arrangement by the protective volume in front of the freezing medium, in particular against the forces acting on freezing.

Preferably, the at least partially flexible wall has a bore, particularly preferably a through hole from an outer side of the wall into a medium-carrying inner region, wherein the pressure sensor is arranged retracted in the bore. So he does not protrude into an inner surface of the wall into this, but rather leaves a distance or a protective volume between its front and the inner surface free. The hole is closed in the area of the inner surface with the flexible wall area, so that the protective volume in the bore between the flexible wall portion on the one hand and the end face of the pressure sensor is disposed on the other hand. The pressure sensor can be inserted into the bore, pressed, screwed, welded, soldered, glued or attached in any other suitable manner. The embodiments described here represent very simple and inexpensive realizations of the sensor arrangement.

An exemplary embodiment of the sensor arrangement is also preferred, which is characterized in that a compressible pressure-conducting medium is arranged in the protective volume. If the flexible wall region is deflected due to the pressure prevailing in the freezing-endangered medium, it acts on the compressible pressure-conducting medium and compresses it. As a result, a pressure in the Druckleitmedium is constructed, which is detectable by the pressure sensor. It is possible that the pressure in the Druckleitmedium deviates from the pressure in the freeze-prone medium in a certain way. In this case, the pressure sensor is preferably appropriately calibrated or operatively connected to a correspondingly calibrated control unit, so that the pressure in the freeze-prone medium can be determined unambiguously on the basis of the detected pressure in the compressible pressure-control medium. In order to realize the most reproducible and accurate pressure measurement, the compressible Druckleitmedium is preferably biased, so even under a defined pressure. In this case, this biasing pressure is preferably smaller than a smallest occurring during operation pressure in the freeze-prone medium, but preferably greater than a normal ambient pressure. As a result, the accuracy of the pressure measurement can be increased.

In any case, it can be seen that the state of the flexible wall region is preferably determined by the pressure in the compressible pressure-conducting medium. The pressure in the compressible Druckleitmedium depends in particular on the deflection of the flexible wall portion.

Alternatively, it is possible for the state of the flexible wall region and in particular its deflection to be determined in another way, for example by an optical measurement, in particular an interference measurement, an ultrasound measurement, a mechanical measurement, or in another suitable manner. The pressure sensor is preferably set up to carry out one of the measurements mentioned.

An exemplary embodiment of the sensor arrangement is preferred, which is characterized in that a gas is provided as the compressible pressure-conducting medium. Particularly preferred is the compressible Druckleitmedium selected from a group consisting of air, nitrogen, a noble gas, in particular argon, and carbon dioxide. A mixture of at least two of the gases mentioned here is possible. Other suitable gases can be used as a compressible Druckleitmedium. A gas as Druckleitmedium provides a cost-effective as well as simple and accurate way to achieve the sensor array. Alternatively, it is also possible that a suitable liquid or a suitable, compressible solid is provided as a compressible Druckleitmedium. In this case, the liquid or the solid must be suitable to translate the pressure in the freeze-prone medium in a precise and reproducible manner into a detectable by the pressure sensor pressure of the compressible Druckleitmediums, so forward to the pressure sensor. Depending on the nature of the Druckleitmediums used, it is obvious that the pressure detected by the pressure sensor is not equal to the pressure in the freeze-prone medium. However, it requires an unambiguous assignment of the pressure values in the freeze-prone medium on the one hand and in the compressible Druckleitmedium other hand, which are preferably stored in a map or as a calibration curve.

An embodiment of the sensor arrangement is also preferred, which is characterized in that the flexible wall region is designed as a membrane. The membrane preferably closes the bore in the wall of the medium-conducting device. Particularly preferably, the membrane terminates flush in its edge regions with the inner surface of the wall. In this way, a flexible wall area, which can also be used damage-free over the long term, can be realized simply and inexpensively.

The object is also achieved by providing a medium-conducting device with at least one sensor arrangement having the features of claim 6. In this case, the sensor arrangement is designed according to one of the embodiments described above. Therefore, in connection with the medium-conducting device, the advantages which have already been described in connection with the sensor arrangement are realized.

In a preferred embodiment, the medium-conducting device is designed as a pump, as a conduit for the freeze-endangered medium, as a metering device or injector for metering or injecting the freeze-endangered medium, and / or as a memory, in particular as a high-pressure accumulator or as a rail for the freeze-endangered medium. In particular, it is possible for the medium-conducting device to be designed as a fore pump or as a high-pressure pump for the freeze-endangered medium. In all areas mentioned here It may be necessary or advantageous to measure a pressure prevailing in the medium which is at risk of freezing, whereby the pressure sensor provided for this purpose is to be protected from freezing medium. As a result, the advantages which have already been described in connection with the sensor arrangement are realized in particular in the stated medium-conducting devices.

The object is also achieved, in which a system for metering a reducing agent into an exhaust gas stream of an internal combustion engine having the features of claim 8 is provided. The system is characterized by at least one medium-conducting device according to one of the previously described embodiments. In the process, the advantages which have already been described in connection with the sensor arrangement and the medium-conducting device are realized for the system.

The system is preferably set up for metering in a urea-water solution into the exhaust gas flow of the internal combustion engine, in particular upstream of a catalytic device, which is set up for the selective catalytic reduction of nitrogen oxides in the exhaust gas. Such devices and catalysts are known per se, so that will not be discussed further. It turns out, however, that in such Reduktionsmitteldosiersystemen typically at least one pressure measuring point is required for control. A pressure sensor provided here can be damaged or destroyed when the reducing agent freezes. This is prevented by means of the sensor arrangement and the medium-conducting device. This happens because the pressure measurement does not take place directly in the freeze-prone medium, but rather indirectly. In this case, the pressure sensor is placed in particular behind a membrane and the protective volume designed in particular as a defined gas volume or air volume. The pressure measurement is then carried out in the compressible Druckleitmedium the protective volume, in particular in the gas. It is preferably provided that the influence of the membrane and / or the influence of Druckleitmediums is corrected to the pressure measurement / are. This can be done by means of a characteristic map or by means of a suitable calibration curve. Upon freezing, a volume expansion of the reducing agent against the membrane and a deflection of the same into the protective volume takes place. The pressure sensor located behind it remains protected. In this way it is protected against frost damage and especially against mechanical destruction by expansion of the freeze-prone medium.

Another advantage is a damping effect of the compressible Druckleitmediums. Especially for the systems discussed here for metering a reducing agent into an exhaust gas stream, oscillating piston pumps are typically used which generate strong and steadily fluctuating pressure signals. By the compressible Druckleitmedium in the protective volume they are damped, so that a smoothed or averaged pressure measurement can be done.

The system preferably includes a backing pump for delivering the reductant from a tank to a high pressure pump, and a high pressure pump provided for thawing and maintaining high pressure in a high pressure region of the system. In particular, the high pressure pump is preferably provided for pressure control in the high pressure region. The system also includes conduits from the tank to the backing pump, from there to the high pressure pump, and from the high pressure pump to at least one metering device, particularly an injector. Typically, a return for the reducing agent from the at least one injector or the at least one metering device to a suitable point of a reducing agent circuit, for example in the tank, to a suction side of the backing pump, to a suction side of the high pressure pump or possibly even in the high pressure region, is provided. It is possible that a plurality of metering devices or injectors from a common high-pressure accumulator, namely a so-called rail, are supplied with reducing agent. As a result, pressure oscillations generated by individual metering events have less effect on the other metering devices or injectors.

In that regard, an embodiment of the system is preferred, which is characterized in that the medium-conducting device as a fore pump, a high-pressure pump, as a conduit for the reducing agent, as a metering device or injector for the reducing agent, and / or as a memory, in particular as a common high-pressure accumulator or rail , is formed for the reducing agent. In this case, a pressure sensor arranged in the region of the pre-pump preferably serves to check whether the backing pump is operating. A pressure sensor arranged in the region of the high-pressure pump, in the high-pressure line or in the high-pressure accumulator preferably serves for pressure monitoring or pressure regulation in the high-pressure region. By means of the pressure sensors described here in the various medium-conducting devices, a suitable monitoring and / or regulation of the system is possible.

The at least partially flexible wall is preferably a wall of the backing pump, the high pressure pump, a line and / or a memory for the reducing agent.

An exemplary embodiment of the system is also preferred, which is characterized in that two sensor arrangements which are designed according to one of the embodiments described above are arranged and arranged in at least one medium-conducting device or also distributed over two medium-conducting devices such that a differential pressure measurement is possible is. In particular, it is possible that one of the sensor arrangements is arranged upstream of a filter for the reducing agent, wherein a second sensor arrangement is arranged downstream of the filter. By suitable differential pressure measurement, a degree of contamination of the filter can be determined or monitored.

The sensor arrangement, in particular the pressure sensor, the medium-conducting device and the system are preferably set up for an operating pressure of at least 1 bar to at most 11 bar absolute, or corresponding to 0 bar to at most 10 bar overpressure. This is a typical operating pressure range for such a system. It turns out that the sensor arrangement is preferably matched to their specific use. For example, during operation of the fore pump, a lower pressure range is provided as the measuring range than in the area of the high-pressure pump or in the high-pressure range downstream of the high-pressure pump. At the same time, the sensor arrangement is preferably set up in order to be able to absorb the pressures occurring when the medium is freezing without damage. In this case, by the expansion of the freezing reducing agent, in particular a freezing urea-water solution, significantly higher pressures than in the operation of the system.

If a measuring range of approximately 5 bar overpressure is provided for the pressure sensor, the compressible pressure-conducting medium is preferably preloaded to approximately 1 bar overpressure in order to allow an accurate pressure measurement.

The object is finally solved by an internal combustion engine having the features of claim 11 is created. This has a system according to one of the embodiments described above. Thus, for the internal combustion engine realize the advantages that have already been explained in connection with the sensor assembly, the medium-conducting device and the system.

The internal combustion engine is preferably designed as a reciprocating engine. In a preferred embodiment, the internal combustion engine is used to drive in particular heavy land or water vehicles, such as mine vehicles, trains, the internal combustion engine is used in a locomotive or a railcar, or ships. It is also possible to use the internal combustion engine to drive a defense vehicle, for example a tank. An exemplary embodiment of the internal combustion engine is preferably also stationary, for example, used for stationary power supply in emergency operation, continuous load operation or peak load operation, the internal combustion engine in this case preferably drives a generator. A stationary application of the internal combustion engine for driving auxiliary equipment, such as fire pumps on oil rigs, is possible. Furthermore, an application of the internal combustion engine in the field of promoting fossil raw materials and in particular fuels, for example oil and / or gas, possible. It is also possible to use the internal combustion engine in the industrial sector or in the field of construction, for example in a construction or construction machine, for example in a crane or an excavator. The internal combustion engine is preferably designed as a diesel engine, as a gasoline engine, as a gas engine for operation with natural gas, biogas, special gas or another suitable gas. In particular, when the internal combustion engine is designed as a gas engine, it is suitable for use in a cogeneration plant for stationary power generation.

The invention will be explained in more detail below with reference to the drawing. The single FIGURE shows an embodiment of an internal combustion engine with a system, a medium-conducting device and a sensor arrangement.

The only Fig. Shows a schematic representation of an embodiment of an internal combustion engine 1 which is a system 3 for dosing a reducing agent in an exhaust stream of the internal combustion engine 1 having. In a manner known per se, the system is preferably set up for metering in a urea-water solution into the exhaust gas stream of an internal combustion engine for the purpose of selectively catalytic reduction of nitrogen oxides in the exhaust gas.

The system 3 has a medium-conducting device 5 on, in the operation - as shown schematically here by an arrow P - by a freezing-endangered medium, namely here the reducing agent, flows through. The medium-conducting device 5 is preferably designed as a backing pump, as a high pressure pump, as a conduit for the reducing agent, as a metering device or injector, and / or as a memory, in particular as a high-pressure accumulator or as a rail, for the reducing agent.

The medium-conducting device 5 has a sensor arrangement 7 with a pressure sensor 9 on. The pressure sensor 9 is set up to measure a pressure in the freeze-endangered Medium, here the reducing agent, prevails. There is basically the problem that freezing reducing agent due to the very high expansion forces the pressure sensor 9 damage or even destroy it mechanically.

To frost damage in the area of the pressure sensor 9 to avoid, indicates the medium-conducting device 5 here an at least partially flexible wall 11 on that with an inner surface 13 is in contact with the freeze-prone medium. The wall 11 has a flexible wall area 15 up, here as a membrane 17 is trained. The pressure sensor 9 is - seen from the freezing medium from - outside the inner surface 13 and in particular outside the flexible wall area 15 arranged, thus by this of the medium-conducting device 5 separated by flowing medium.

In particular, the pressure sensor 9 in the wall 11 arranged and from the flexible wall area 15 through a protective volume 19 spaced. For this purpose, the wall 11 prefers a hole 21 on, which is designed in particular as a through hole, and which the wall 11 up to the inner surface 13 interspersed. The pressure sensor 9 is in the hole 21 arranged withdrawn, and the bore 21 is through the flexible wall area 15 , here through the membrane 17 , to the inner surface 13 closed off. This includes the flexible wall area 15 preferably flush with the inner surface 13 from. The protective volume 19 is thus between an end face 23 of the pressure sensor 9 and the flexible wall area 15 arranged. In this way, the front side 23 of the pressure sensor 9 and thus also this overall protected from the effects of the freezing medium, in this case in particular the freezing reducing agent.

In the protective volume 19 a compressible Druckleitmedium is preferably arranged, in particular a gas. These are preferably air, nitrogen, a noble gas, in particular argon, and / or carbon dioxide. Other suitable gases or mixtures of these or other gases are possible. Finally, it is alternatively or additionally also possible that a compressible liquid or a compressible solid in the protective volume 19 is arranged.

The compressible Druckleitmedium is preferably in the protective volume 19 at a predetermined, defined biasing pressure, which then prevails when the freeze-prone medium in the medium-conducting device 5 under normal pressure, ie at 1 bar absolute or corresponding to 0 bar overpressure.

In a preferred embodiment, it is provided that the biasing pressure in the protective volume 19 smaller than a smallest in the operation of the system 3 occurring operating pressure of the freeze-prone medium, in this case the reducing agent, which allows a particularly accurate and reproducible pressure measurement. This is indicated in the figure by the fact that the membrane 17 inside in the protective volume 19 is shown arched into it. Alternatively, it is also possible that the biasing pressure in the protective volume 19 just a minimum operating pressure of the system 3 in the field of medium-conducting device 5 equivalent. It is then possible that the membrane 17 in normal operation of the medium-conducting device 5 has no or only a very small curvature. Finally, an embodiment is possible in which the biasing pressure in the protective volume 19 is greater than the smallest expected operating pressure in the medium-conducting device 5 during operation of the system 3 , In this case, the membrane 17 typically inverted as shown in the figure arched, namely from the protective volume 19 out.

Regardless of the specifically selected biasing pressure is the operation of the sensor assembly 7 the following: Depending on the pressure in the freeze-prone medium, the deflection of the flexible wall area changes 15 , here the membrane 17 , which increases the pressure in the protective volume 19 established. The pressure sensor 9 recorded in particular with its front side 23 the pressure in the protective volume 19 and thus, at least indirectly, also the pressure prevailing in the freezing-endangered medium, here in the reducing agent. It is preferably a map or a calibration curve in the pressure sensor 9 itself or stored in a control unit, by the clear pressure in the freezing medium, here the reducing agent, on the basis of the pressure sensor 9 measured pressure in the protective volume 19 is determinable.

Through a pump of the system 3 caused discontinuities in a time-dependent considered pressure curve, in particular pressure surges are due to the damping effect of the protection volume 19 filtered, so that a less fluctuating pressure curve through the pressure sensor 9 is measured. This provides a further advantage of the sensor arrangement 7 represents.

Freezes the medium, in particular the reducing agent, in the medium-conducting device 5 , the expansion forces that occur act on the flexible wall area 15 , in particular on the membrane 17 , The pressure sensor 9 is thereby by the protective volume 19 protected against the immediate action of these expansion forces and thus against frost damage.

Overall, it is thus evident that the sensor arrangement 7 , the medium-conducting device 5 , the system 3 and the internal combustion engine 1 in a particularly advantageous, simple and cost-effective manner against frost damage by freezing medium in the region of the pressure sensor 9 are protected.

Claims (11)

Sensor arrangement ( 7 ) for pressure measurement in a freeze-prone medium, with a medium-conducting device ( 5 ), which is an at least partially flexible wall ( 11 ), wherein a pressure sensor ( 9 ) by a flexible wall area ( 15 ) from a medium-conducting device ( 5 ) is arranged and adapted to a pressure in the medium based on a state of the flexible wall region ( 15 ) to eat. Sensor arrangement ( 7 ) according to claim 1, characterized in that the pressure sensor ( 9 ) in the wall ( 11 ) of the medium-conducting device ( 5 ) and of the flexible wall area ( 15 ) by a protective volume ( 19 ) is spaced. Sensor arrangement ( 7 ) according to one of the preceding claims, characterized in that in the protective volume ( 19 ) A compressible Druckleitmedium is arranged. Sensor arrangement ( 7 ) according to one of the preceding claims, characterized in that the compressible Druckleitmedium is a gas. Sensor arrangement ( 7 ) according to one of the preceding claims, characterized in that the flexible wall area ( 15 ) as a membrane ( 17 ) is trained. Medium-conducting device ( 5 ), characterized by at least one sensor arrangement ( 7 ) according to one of claims 1 to 5. Medium-conducting device ( 5 ) according to claim 6, characterized in that the medium-conducting device is designed as a pump, as a conduit for the freeze-endangered medium, as a metering device or injector for the freeze-endangered medium, and / or as a memory for the freeze-endangered medium. System ( 3 ) for metering a reducing agent into an exhaust gas stream of an internal combustion engine ( 1 ), characterized by at least one medium-conducting device ( 5 ) according to one of claims 6 and 7. System ( 3 ) according to claim 8, characterized in that the at least one medium-conducting device ( 5 ) is designed as a backing pump, as a high-pressure pump, as a conduit for the reducing agent, as a metering device or injector for the reducing agent, and / or as a memory for the reducing agent. System ( 3 ) according to one of claims 8 and 9, characterized in that two sensor arrangements ( 7 ) according to one of claims 1 to 5 in at least one medium-conducting device ( 5 ) are arranged in a suitable manner for differential pressure measurement. Internal combustion engine ( 1 ), characterized by a system ( 3 ) according to any one of claims 8 to 10.

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