Patent ID: 12259291

Like or functionally equivalent elements are denoted in all the figures by the same reference numerals and in part are not described separately.

FIG.1illustrates a schematic representation of a system for the exhaust gas aftertreatment of a motor vehicle20, comprising an apparatus10for determining an amplitude A of a pump-induced fluid pressure fluctuation SVarof a fluid1(in this case for example a reducing agent) in accordance one embodiment of the present disclosure. Fundamentally, the system has for the exhaust gas aftertreatment in this case a tank6for storing and/or providing a, preferably liquid, reducing agent (for example ammonia or aqueous urea solution). Reducing agent can be removed from this tank6by means of the pump2, which is in fluid connection with the tank6by way of corresponding conveying lines, and conveyed (likewise by way of corresponding conveying lines) to a metering device3in the form of a metering valve. In other words, the pump2can be in fluid connection with the tank6on the input side and with the metering device3on the output side.

By means of the metering device3, the reducing agent can then be introduced or sprayed into exhaust gas flow that is conveyed in the exhaust gas tract5. In this case, in addition to the configuration of the metering device3itself, the reducing agent pressure that is applied at the metering device3is also decisive for regulating the metering parameters (amount, spray jet shape, etc.). A procedure of regulating this reducing agent pressure to a predetermined target pressure psollcan take place, for example, by way of a corresponding control or regulation procedure of the pump rotational speed. For this purpose, the system for exhaust gas aftertreatment can comprise a control unit11, which is preferably configured together with the apparatus10as a structural unit for the amplitude determination. This control unit11can provide a pressure signal S (cf.FIG.2), wherein the pressure signal S can be a prevailing fluid pressure of the reducing agent and/or can be a variable from which the prevailing fluid pressure of the reducing agent can be derived.

So as to provide the relevant pressure signal S, the system that is illustrated inFIG.1comprises for the exhaust gas aftertreatment a sensor device4that is arranged on the output side of the pump2and is configured so as to detect and provide the relevant pressure signal S. On the basis of this pressure signal S and by means of a regulating method—already known in the prior art—the control unit11can then be embodied so as to output relevant control signals to the pump2in order thereby to regulate the pump rotational speed and consequently the pressure of the reducing agent on the output side. In addition, the reducing agent pressure can also be regulated by way of an optional return line—shown here—to the tank6with a restrictor7that is arranged there.

In addition to controlling the pump speed so as to regulate the reducing agent pressure, the pressure signal S that is detected and provided by the sensor device4(seeFIG.2) is also used to determine and check the plausibility of the amplitude A of the pump-induced fluid pressure fluctuation SVarof the reducing agent. For this purpose, the system for the exhaust gas aftertreatment has a corresponding apparatus10for determining an amplitude A of a pump-induced fluid pressure fluctuation SVarof a fluid1, which is regulated to a target fluid pressure psollby means of a pump2, in accordance with one embodiment of the present disclosure. This apparatus10, which can be embodied, for example, as part of a control unit of the motor vehicle20, is configured in this case so as to perform a method that is described in greater detail below—with reference toFIG.4. The apparatus10can in this case comprise for example a programmed microprocessor and a corresponding memory storage device. In an advantageous manner, the memory storage device holds instructions are can be implemented by the processor, as a result of which the apparatus10is overall in the position to perform the previously described method.

FIG.2illustrates exemplary measurement values of a pressure signal S of a fluid1as a function of time, and said pressure signal can be used for determining the amplitude A of a pump-induced fluid pressure fluctuation SVarof a fluid1. For example, the illustrated pressure signal may have been detected and provided by means of the sensor device4that is illustrated inFIG.1. In this case,FIG.2illustrates the time course of the pump output-side fluid pressure of a fluid1during three short metering processes (cf. logical metering signal D), wherein the fluid pressure is regulated by varying the pump rotational speed to a target fluid pressure psollof almost 10 bar. In addition to the brief pressure drops SD1, SD2, SD3of about 0.2 bar while metering is taking place, the dynamic change (=pump-induced fluid pressure fluctuation SVar) in the fluid pressure around psollthat is caused by the periodic pump movement can also be seen inFIG.2. In this case, the reliable determination of the amplitude A, in other words the size, of this pump-induced fluid pressure fluctuation SVaris the subject of the method initially described in general with reference toFIG.4.

FIG.4illustrates a flow diagram for illustrating a method for determining an amplitude A of a pump-induced fluid pressure fluctuation SVarof a fluid1, which is regulated to a target fluid pressure psollby means of a pump2, in accordance with one embodiment of the present disclosure. The fluid1can be, for example, a reducing agent for exhaust gas aftertreatment, such as for example ammonia or aqueous urea solution. In step S1, a pressure signal S of the fluid is provided, comprising a plurality of pressure signal values in a predetermined time interval. In this case, the pressure signal S can indicate a fluid pressure of the fluid1and/or be a variable from which the fluid pressure of the fluid1can be derived. For example, the provided pressure signal S in a predetermined time interval can be the curve illustrated inFIG.2. In step S2, the amplitude A of the fluid pressure fluctuation SVaris determined on the basis of the provided pressure signal S, for example, on the basis of a difference between a maximum pressure signal value Dmaxand a minimum pressure signal value Dminof the provided pressure signal S, wherein possible calculation rules for determining the amplitude will be discussed in detail in connection with the description ofFIGS.3and5. In step S3, a check is subsequently performed as to whether the provided pressure signal S satisfies a predetermined plausibility criterion. Accordingly, this step can also be referred to as a validation and/or a plausibility check in order to thereby identify obvious inaccuracies in the amplitude determination procedure in step S2. For example, the predetermined plausibility criterion can also include the condition as to whether the pressure signal S has just not been detected during a metering process that greatly falsifies the pressure curve. Then, in step S4, the determined amplitude A is output if the provided pressure signal S satisfies the plausibility criterion. However, if the provided pressure signal S does not satisfy the plausibility criterion, the determined amplitude A is rejected in step S4.

In connection with the above-mentioned method steps of determining (S2) and checking (S3),FIG.3shows a schematic representation which illustrates these method steps in accordance with a first embodiment of the present disclosure. In this case, a maximum and minimum pressure signal value Dmaxand Dminof the provided pressure signal S is initially determined within a first time segment t1(t1≈0.3 s). In other words, the largest and smallest pressure signal value is determined within the first time segment t1of the pressure signal S. On the basis of these values, it is possible to calculate the amplitude A for example by way of A=|Dmax−Dmin|2. Alternatively, however, other calculation rules, such as for example the geometric mean of Dmaxand Dmincan be used.

Then, within a second time segment t2(t2≈0.5 s) that follows the first time segment t1(in this case immediately adjoining), a first number N1of pressure signal values is determined which are within a first pressure band Δ1(Δ1≈20 mbar) around the maximum pressure signal value Dmaxand a second number N2of pressure signal values is determined which lie within a second pressure band Δ2(Δ2≈20 mbar) around the minimum pressure signal value Dmin. In this context, the first and second pressure band Δ1, Δ2can thus also be referred to as the first and second tolerance range, respectively. In so doing, if the determined first number N1exceeds a first threshold value S1(for example S1=3) and the determined second number N2exceeds a second threshold value S2(for example S1=3) (plausibility criterion), the previously determined amplitude A is to be the output (S5). For this purpose, the method includes the step of checking whether the pressure signal S that is provided satisfies a predetermined plausibility criterion. In other words, it is possible thereby to perform a check or validation as to whether the previously determined amplitude (estimated) value is actually a representative value for the prevailing system state with the result that overall the reliability of the method is increased.

In order to increase this even further, the aforementioned checking procedure can also include determining whether within the second time segment t2at least one pressure signal value is above the predetermined first pressure band Δ1around the maximum pressure signal value Dmaxand/or whether at least one pressure signal value is below the predetermined second pressure band Δ2around the minimum pressure signal value Dmin. This means, in other words, the plausibility criterion also includes in addition the condition that within the second time segment t2there is no pressure signal value with a value greater than the upper pressure band limit value Δ1oof the predetermined first pressure band Δ1and/or less than the lower pressure band limit value Δ2uof the predetermined second pressure band Δ2. If so, the determined amplitude A is not to be output and instead is to be rejected. In addition, the plausibility criterion can also include further conditions, for example a check can be performed as to whether the pressure signal S does not include any pressure drops or other artifacts which falsify the amplitude determination. Overall, the aforementioned plausibility check can advantageously increase the reliability of the amplitude determination procedure, wherein the amplitude determination procedure in turn can form the basis for a further diagnosis of the fluid system. Information regarding the rigidity of the system and thus information regarding the possible presence of leaks or other malfunctions in the system can thus be obtained from the determined or output amplitude A.

FIG.5shows a schematic representation that illustrates the method steps of the determining procedure (S2) and checking procedure (S3) in accordance with a second embodiment of the present disclosure. For this purpose, the same pressure signal range as discussed above in connection withFIG.3is shown in diagram a ofFIG.5. In lieu of the subdivision into the time segments t1and t2, the sliding pressure signal mean value M forms the basis for determining the amplitude. The sliding pressure signal mean value M represents in this case the average of multiple pressure signal values—in the current case the last 10—preceding a “respective pressure signal value”, in other words temporally earlier, pressure signal values. In this case, the sliding pressure signal mean value M shifts or moves with the respectively considered “respective pressure signal value” with the result that always the same number of pressure signal values (in this case 10) are included in the calculation of the respective value of the sliding pressure signal mean value M.

The amplitude A is then determined on the basis of the mean absolute deviation of the pressure signal values of the pressure signal S with respect to the sliding pressure signal mean value M. To this end, initially the deviation or the distance d (indicated by the double arrow) of each pressure signal value of the pressure signal S is determined with respect to a value, which is associated with the respective pressure signal value, of the sliding pressure signal mean value M, wherein the result of this arithmetic operation is illustrated for example in diagram b ofFIG.5. Then the absolute amount |d| of the respective values of the distance d, which is shown in diagram c, is formed. Based on this, the arithmetic mean of a plurality (in the present case, for example 100) of these absolute values |d| is formed, which in the present case includes the respective summation of the last 100 absolute values |d| and then dividing by the number of summands (here 100). Alternatively, however, the plurality can also comprise a different number of values, for example 50 or 200. The conversion into an amplitude value is then carried out by multiplying by the factor π/2.

Analogous to the sliding pressure signal mean value M, in this case the mean absolute deviation of the pressure signal values can also be calculated in a sliding or moving manner. In other words, a mean absolute deviation can be calculated at multiple, preferably successive, points of the pressure signal S, wherein the same number of temporally earlier absolute deviations are included in the calculation of the respective value of the sliding mean absolute deviation. In other words, a quasi-continuous calculation of the mean absolute deviation and thus a quasi-continuous determination of the amplitude A can take place, wherein in this context the above mentioned summation can also be understood as integration.

The plausibility check or the checking as to whether the pressure signal S that is provided satisfies a predetermined plausibility criterion can take place according to this embodiment on the basis of the distance d (diagram b). For this purpose, the step of checking (S3) can include determining a sum of a plurality of, preferably successive, values of the distance d. In other words, the checking procedure can include determining a sum of signed deviations of the plurality of pressure signal values of the pressure signal S with respect to the moving pressure signal mean value M. In this case, the amplitude A is preferably only then to be output if the sum of signed deviations is equal to 0 or less than a predetermined threshold value (for example. 5 mbar). In other words, the provided pressure signal S is to satisfy the predetermined plausibility criterion if the sum of signed deviations is equal to 0 or less than a predetermined threshold value. In this case, this checking step advantageously ensures that the output amplitude value of the pump-induced fluid pressure fluctuation SVarindicates the deviation with respect to a quasi-stationary mean value or that a quasi-stationary state is present.

FIG.6illustrates a schematic representation of a motor vehicle20having an apparatus10for determining an amplitude A of a pump-induced fluid pressure fluctuation SVarof a fluid1, which is regulated to a target fluid pressure psollby means of a pump2, in accordance with one embodiment of the present disclosure. In the present case, the motor vehicle20is an articulated vehicle, in other words a combination of a tractor unit and a semi-trailer. In this case, the motor vehicle20comprises, inter alia, a pump2, wherein a fluid pressure of a fluid2, preferably a fluid pressure of a reducing agent for exhaust gas aftertreatment, is regulated to a target fluid pressure psollby means of the pump2. For example, the fluid pressure can be regulated in this case by varying the pump speed. In addition, the motor vehicle20comprises a device10for determining the pump-induced fluid pressure fluctuation SVarof the fluid1, preferably for determining the pump-induced fluctuation in the reducing agent pressure. The apparatus10is configured in this case so as to perform a method as described in this document. For this purpose, the apparatus10can also comprise a sensor device4which is configured so as to detect and provide the corresponding pressure signal. For example, the apparatus10can comprise a pressure sensor4for this purpose.

Although the present disclosure includes reference to specific exemplary embodiments, it is evident to the person skilled in the art that different changes can be performed and equivalents used as alternatives without abandoning the scope of the present disclosure. As a consequence, the present disclosure is not to be limited to the disclosed exemplary embodiments but rather is to include all exemplary embodiments that fall into the scope of the attached claims. In particular, the present disclosure also claims protection for the subject matter and the features of the subordinate claims independently from the claims included by reference.

LIST OF REFERENCE NUMERALS

1Fluid2Pump3Metering device4Sensor device5Exhaust gas tract6Tank7Restrictor10Apparatus for determining the rotational speed11Control unit20Motor vehicleSD1,SD2,SD3Pressure dropsD Metering signald Distance|d| Absolute amount of the distanceM Sliding pressure signal mean valueS Pressure signalSVarPump-induced fluid pressure variationΔ1oUpper pressure band limit valueΔ2uLower pressure band limit value