METHOD AND DEVICE FOR DETERMINING AN AMPLITUDE OF A PUMP-INDUCED FLUID PRESSURE FLUCTUATION OF A FLUID

Abstract

The invention relates to a method for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid which is regulated to a desired fluid pressure p.sub.soll by means of a pump. In this case, the method comprises providing (S1) a pressure signal of the fluid, determining (S2) the amplitude A of the fluid pressure fluctuation on the basis of the pressure signal which has been provided, checking (S3) whether the pressure signal which has been provided satisfies a predetermined plausibility criterion, and outputting or rejecting (S4) the determined amplitude A on the basis of whether the pressure signal which has been provided satisfies the predetermined plausibility criterion. This advantageously provides a combined method in which, in addition to fundamentally determining the amplitude A of a fluid pressure fluctuation, a plausibility check is also carried out immediately in order to determine whether this fluid pressure fluctuation also actually corresponds to a representative value for the current system state. Furthermore, the invention also relates to a device which is designed to carry out the above-mentioned method and to a motor vehicle having a corresponding device.

Claims

1-15. (canceled)

16. A method for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid that is regulated by means of a pump to a target fluid pressure p.sub.soll, comprising the steps: providing a pressure signal of the fluid that comprises multiple pressure signal values in a predetermined time interval; determining the amplitude A of the pump-induced fluid pressure fluctuation on the basis of the provided pressure signal; checking whether the provided pressure signal satisfies the predetermined plausibility criterion; and outputting the determined amplitude A if the provided pressure signal satisfies the predetermined plausibility criterion and rejecting the determined amplitude A if the provided pressure signal does not satisfy the predetermined plausibility criterion.

17. The method as claimed in claim 16, characterized in that: the pump-induced fluid pressure fluctuation of a fluid is periodic; or the plausibility criterion characterizes a quasi-stationary state.

18. The method as claimed in claim 16, characterized in that: a) the fluid is a reducing agent for exhaust gas treatment; or b) the pump-induced fluid pressure fluctuation is a periodic and/or sinusoidal fluid pressure oscillation that is caused by the operation of the pump; or c) the method includes determining a system rigidity on the basis of the determined and/or output amplitude A.

19. The method as claimed in claim 16, characterized in that the procedure of determining the amplitude A includes the steps: determining a maximum and minimum pressure signal value D.sub.max and D.sub.min of the provided pressure signal within a first time segment t.sub.1 of the predetermined time interval; and calculating the amplitude A on the basis of the determined maximum and minimum pressure signal values D.sub.max and D.sub.min.

20. The method as claimed in claim 19, characterized in that the checking procedure includes the following steps: determining a first number N.sub.1 of pressure signal values which lie within a second time segment t.sub.2 that follows the first time segment t.sub.1 in a predetermined first pressure band Δ.sub.1 around the maximum pressure signal value D.sub.max; or determining a second number N.sub.2 of pressure signal values which lie within the second time segment t.sub.2 in a predetermined second pressure band Δ.sub.2 around the minimum pressure signal value D.sub.min; and that the provided pressure signal satisfies the predetermined plausibility criterion if the first number N.sub.1 exceeds a first threshold value S.sub.1 and/or the second number N.sub.2 exceeds a second threshold value S.sub.2.

21. The method as claimed in claim 20, characterized in that the checking procedure includes the following steps: a1) determining whether within the second time segment t.sub.2 at least one pressure signal value lies above the predetermined first pressure band Δ.sub.1 around the maximum pressure signal value D.sub.max; or a2) determining whether within the second time segment t.sub.2 at least one pressure signal value lies below the predetermined second pressure band Δ.sub.2 around the minimum pressure signal value D.sub.min; and b) that the provided pressure signal satisfies the predetermined plausibility criterion if no pressure signal value is above the predetermined first pressure band Δ.sub.1 around the maximum pressure signal value D.sub.max and/or no pressure signal value is below the predetermined second pressure band Δ.sub.2 around the minimum pressure signal value D.sub.min.

22. The method as claimed in claim 20, characterized in that: a) the predetermined first pressure band Δ.sub.1 is centered around the maximum pressure signal value D.sub.max and the predetermined second pressure band Δ.sub.2 is centered around the minimum pressure signal value D.sub.min; or b) the predetermined first pressure band Δ.sub.1 and/or the predetermined second pressure band Δ.sub.2 have a width that is defined on the basis of the determined maximum and/or minimum pressure signal values D.sub.max and/or D.sub.min; or c) the predetermined first pressure band Δ.sub.1 has the same width as the predetermined second pressure band Δ.sub.2.

23. The method as claimed in claim 22, characterized in that the predetermined first pressure band Δ.sub.1 and/or the predetermined second pressure band Δ.sub.2 have a width defined essentially as 0.2% of the maximum or minimum D.sub.max or D.sub.min.

24. The method as claimed in claim 19, characterized in that: a) the first time segment t.sub.1 is shorter than the second time segment t.sub.2; or b) the first time segment t.sub.1 and/or the second time segment t.sub.2 is longer than 0.1 s.

25. The method as claimed in claim 24, characterized in that the first time segment t.sub.1 and/or the second time segment t.sub.2 is longer than 0.5 s.

26. The method as claimed in claim 16, characterized in that the procedure of determining the amplitude A includes the following step: calculating the amplitude A on the basis of a mean absolute deviation of a plurality of pressure signal values of the provided pressure signal with respect to a sliding pressure signal mean.

27. The method as claimed in claim 26, characterized in that the mean absolute deviation is a sliding mean absolute deviation.

28. The method as claimed in claim 26, characterized in that the checking procedure includes the following step: determining a sum of signed deviations of the plurality of pressure signal values of the pressure signal with respect to the sliding pressure signal mean value; and that the provided pressure signal satisfies the predetermined plausibility criterion if the sum of signed deviations is equal to 0 or less than a predetermined threshold value.

29. The method as claimed in claim 28, characterized in that the plurality of pressure signal values includes a plurality of successive pressure signal values.

30. The method as claimed in claim 26, characterized in that the procedure of calculating the amplitude A includes the following steps: calculating an associated value of the sliding pressure signal mean value with respect to each pressure signal value of the plurality of pressure signal values on the basis of multiple pressure signal values that precede the respective pressure signal value; and calculating an absolute deviation of each pressure signal value of the plurality of pressure signal values with respect to the associated value of the sliding pressure signal mean value.

31. The method as claimed in claim 30, characterized in that the multiple pressure signal values directly precede the respective pressure signal value.

32. The method as claimed in claim 26, characterized in that a) the plurality of pressure signal values comprise at least 10 successive pressure signal values; or b) the sliding pressure signal mean value is based on a previously specified number of pressure signal values and/or on pressure signal values in a specified time interval.

33. The method as claimed in claim 32, characterized in that the plurality of pressure signal values comprise at least 100 successive pressure signal values.

34. The method as claimed in claim 16, characterized in that a clocked operation in which the method is carried out at regular time intervals.

35. The method as claimed in claim 34, characterized in that: a) the regular time intervals correspond to the predetermined time interval; or b) the determined amplitude A of the pump-induced fluid pressure fluctuation is output after the regular time intervals have elapsed.

36. The method as claimed in claim 16, characterized in that the fluid that is regulated to a target fluid pressure p.sub.soll can be metered by means of a metering device and the provided pressure signal is a pressure signal during an operating phase of the metering device in which metering does not take place.

37. An apparatus for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid, wherein the apparatus is configured so as to perform a method as claimed in claim 16.

38. The apparatus of claim 37 further comprising a sensor device which is configured so as to detect and provide the pressure signal.

39. A motor vehicle, comprising an apparatus for determining an amplitude of a pump-induced fluid pressure fluctuation of a fluid, as claimed in claim 37.

Description

[0035] The previously described aspects and advantages of the present disclosure can be combined in any manner with one another. Further details and advantages of the present disclosure are described below with reference to the attached drawings. In the drawings:

[0036] FIG. 1 shows a schematic representation of a system for the exhaust gas aftertreatment of a motor vehicle, comprising an apparatus for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid in accordance with an embodiment of the present disclosure;

[0037] FIG. 2 shows exemplary measurement values of a pressure signal of a fluid as a function of time, and said pressure signal can be used for determining in accordance with the present disclosure an amplitude A of a pump-induced fluid pressure fluctuation of a fluid;

[0038] FIG. 3 shows a schematic representation that illustrates the method steps of determining and checking procedures in accordance with a first embodiment of the present disclosure;

[0039] FIG. 4 shows a flow diagram so as to illustrate the method for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid in accordance with one embodiment of the present disclosure;

[0040] FIG. 5 shows a schematic representation that illustrates the method steps of the determining and checking procedures in accordance with a second embodiment of the present disclosure; and

[0041] FIG. 6 shows a schematic representation of a motor vehicle having an apparatus for determining an amplitude A of a pump-induced fluid pressure fluctuation of a fluid in accordance one embodiment of the present disclosure.

[0042] Like or functionally equivalent elements are denoted in all the figures by the same reference numerals and in part are not described separately.

[0043] FIG. 1 illustrates a schematic representation of a system for the exhaust gas aftertreatment of a motor vehicle 20, comprising an apparatus 10 for determining an amplitude A of a pump-induced fluid pressure fluctuation S.sub.Var of a fluid 1 (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 tank 6 for storing and/or providing a, preferably liquid, reducing agent (for example ammonia or aqueous urea solution). Reducing agent can be removed from this tank 6 by means of the pump 2, which is in fluid connection with the tank 6 by way of corresponding conveying lines, and conveyed (likewise by way of corresponding conveying lines) to a metering device 3 in the form of a metering valve. In other words, the pump 2 can be in fluid connection with the tank 6 on the input side and with the metering device 3 on the output side.

[0044] By means of the metering device 3, the reducing agent can then be introduced or sprayed into exhaust gas flow that is conveyed in the exhaust gas tract 5. In this case, in addition to the configuration of the metering device 3 itself, the reducing agent pressure that is applied at the metering device 3 is 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 p.sub.soll can 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 unit 11, which is preferably configured together with the apparatus 10 as a structural unit for the amplitude determination. This control unit 11 can 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.

[0045] So as to provide the relevant pressure signal S, the system that is illustrated in FIG. 1 comprises for the exhaust gas aftertreatment a sensor device 4 that is arranged on the output side of the pump 2 and 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 unit 11 can then be embodied so as to output relevant control signals to the pump 2 in 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 tank 6 with a restrictor 7 that is arranged there.

[0046] 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 device 4 (see FIG. 2) is also used to determine and check the plausibility of the amplitude A of the pump-induced fluid pressure fluctuation S.sub.Var of the reducing agent. For this purpose, the system for the exhaust gas aftertreatment has a corresponding apparatus 10 for determining an amplitude A of a pump-induced fluid pressure fluctuation S.sub.Var of a fluid 1, which is regulated to a target fluid pressure p.sub.soll by means of a pump 2, in accordance with one embodiment of the present disclosure. This apparatus 10, which can be embodied, for example, as part of a control unit of the motor vehicle 20, is configured in this case so as to perform a method that is described in greater detail below—with reference to FIG. 4. The apparatus 10 can 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 apparatus 10 is overall in the position to perform the previously described method.

[0047] FIG. 2 illustrates exemplary measurement values of a pressure signal S of a fluid 1 as a function of time, and said pressure signal can be used for determining the amplitude A of a pump-induced fluid pressure fluctuation S.sub.Var of a fluid 1. For example, the illustrated pressure signal may have been detected and provided by means of the sensor device 4 that is illustrated in FIG. 1. In this case, FIG. 2 illustrates the time course of the pump output-side fluid pressure of a fluid 1 during 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 p.sub.soll of almost 10 bar. In addition to the brief pressure drops S.sub.D1, S.sub.D2, S.sub.D3 of about 0.2 bar while metering is taking place, the dynamic change (=pump-induced fluid pressure fluctuation S.sub.Var) in the fluid pressure around p.sub.soll that is caused by the periodic pump movement can also be seen in FIG. 2. In this case, the reliable determination of the amplitude A, in other words the size, of this pump-induced fluid pressure fluctuation S.sub.Var is the subject of the method initially described in general with reference to FIG. 4.

[0048] FIG. 4 illustrates a flow diagram for illustrating a method for determining an amplitude A of a pump-induced fluid pressure fluctuation S.sub.Var of a fluid 1, which is regulated to a target fluid pressure p.sub.soll by means of a pump 2, in accordance with one embodiment of the present disclosure. The fluid 1 can 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 fluid 1 and/or be a variable from which the fluid pressure of the fluid 1 can be derived. For example, the provided pressure signal S in a predetermined time interval can be the curve illustrated in FIG. 2. In step S2, the amplitude A of the fluid pressure fluctuation S.sub.Var is determined on the basis of the provided pressure signal S, for example, on the basis of a difference between a maximum pressure signal value D.sub.max and a minimum pressure signal value D.sub.min of the provided pressure signal S, wherein possible calculation rules for determining the amplitude will be discussed in detail in connection with the description of FIGS. 3 and 5. 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.

[0049] In connection with the above-mentioned method steps of determining (S2) and checking (S3), FIG. 3 shows 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 D.sub.max and D.sub.min of the provided pressure signal S is initially determined within a first time segment t.sub.1 (t.sub.1≈0.3 s). In other words, the largest and smallest pressure signal value is determined within the first time segment t.sub.1 of the pressure signal S. On the basis of these values, it is possible to calculate the amplitude A for example by way of A=|D.sub.max−D.sub.min|2. Alternatively, however, other calculation rules, such as for example the geometric mean of D.sub.max and D.sub.min can be used.

[0050] Then, within a second time segment t.sub.2 (t.sub.2≈0.5 s) that follows the first time segment t.sub.1 (in this case immediately adjoining), a first number N.sub.1 of pressure signal values is determined which are within a first pressure band Δ.sub.1 (Δ.sub.1≈20 mbar) around the maximum pressure signal value D.sub.max and a second number N.sub.2 of pressure signal values is determined which lie within a second pressure band Δ.sub.2 (Δ.sub.2≈20 mbar) around the minimum pressure signal value D.sub.min. In this context, the first and second pressure band Δ.sub.1, Δ.sub.2 can thus also be referred to as the first and second tolerance range, respectively. In so doing, if the determined first number N.sub.1 exceeds a first threshold value S.sub.1 (for example S.sub.1=3) and the determined second number N.sub.2 exceeds a second threshold value S.sub.2 (for example S.sub.1=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.

[0051] In order to increase this even further, the aforementioned checking procedure can also include determining whether within the second time segment t.sub.2 at least one pressure signal value is above the predetermined first pressure band Δ.sub.1 around the maximum pressure signal value D.sub.max and/or whether at least one pressure signal value is below the predetermined second pressure band Δ.sub.2 around the minimum pressure signal value D.sub.min. This means, in other words, the plausibility criterion also includes in addition the condition that within the second time segment t.sub.2 there is no pressure signal value with a value greater than the upper pressure band limit value Δ1.sup.o of the predetermined first pressure band Δ.sub.1 and/or less than the lower pressure band limit value Δ.sub.2.sup.u of the predetermined second pressure band Δ.sub.2. 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.

[0052] FIG. 5 shows 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 with FIG. 3 is shown in diagram a of FIG. 5. In lieu of the subdivision into the time segments t.sub.1 and t.sub.2, 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.

[0053] 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 of FIG. 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.

[0054] 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.

[0055] 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 S.sub.Var indicates the deviation with respect to a quasi-stationary mean value or that a quasi-stationary state is present.

[0056] FIG. 6 illustrates a schematic representation of a motor vehicle 20 having an apparatus 10 for determining an amplitude A of a pump-induced fluid pressure fluctuation S.sub.Var of a fluid 1, which is regulated to a target fluid pressure p.sub.soll by means of a pump 2, in accordance with one embodiment of the present disclosure. In the present case, the motor vehicle 20 is an articulated vehicle, in other words a combination of a tractor unit and a semi-trailer. In this case, the motor vehicle 20 comprises, inter alia, a pump 2, wherein a fluid pressure of a fluid 2, preferably a fluid pressure of a reducing agent for exhaust gas aftertreatment, is regulated to a target fluid pressure p.sub.soll by means of the pump 2. For example, the fluid pressure can be regulated in this case by varying the pump speed. In addition, the motor vehicle 20 comprises a device 10 for determining the pump-induced fluid pressure fluctuation S.sub.Var of the fluid 1, preferably for determining the pump-induced fluctuation in the reducing agent pressure. The apparatus 10 is configured in this case so as to perform a method as described in this document. For this purpose, the apparatus 10 can also comprise a sensor device 4 which is configured so as to detect and provide the corresponding pressure signal. For example, the apparatus 10 can comprise a pressure sensor 4 for this purpose.

[0057] 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

[0058] 1 Fluid

[0059] 2 Pump

[0060] 3 Metering device

[0061] 4 Sensor device

[0062] 5 Exhaust gas tract

[0063] 6 Tank

[0064] 7 Restrictor

[0065] 10 Apparatus for determining the rotational speed

[0066] 11 Control unit

[0067] 20 Motor vehicle

[0068] S.sub.D1,S.sub.D2,S.sub.D3 Pressure drops

[0069] D Metering signal

[0070] d Distance

[0071] |d| Absolute amount of the distance

[0072] M Sliding pressure signal mean value

[0073] S Pressure signal

[0074] S.sub.Var Pump-induced fluid pressure variation

[0075] Δ.sub.1.sup.o Upper pressure band limit value

[0076] Δ.sub.2.sup.u Lower pressure band limit value