Method for diagnosing a quality signal, control device, control device program and control device program product

Abstract

A method for diagnosing a quality signal (26). The quality signal (26) is provided by a quality sensor (24) used in a reagent metering system (10). The reagent metering system (10) meters a urea/water solution (14) stored in a tank (12), the quality of which is checked by the quality sensor (24), upstream of an SCR catalytic converter (20).

Claims

1. A method for diagnosing a quality signal (26) provided by a quality sensor (24) used in a reagent metering system (10), wherein the reagent metering system (10) meters a urea/water solution (14) stored in a tank (12) the quality of the urea/water solution (14) is checked by the quality sensor (24), upstream of an SCR catalytic converter (20), wherein the quality sensor (24) includes a signal-processor (34) having a clock generator (36) which provides a clock signal (38), wherein the quality sensor (24) ascertains the quality signal (26) on the basis of a time-based measurement, the method comprising: transmitting the quality signal (26) to a controller (28) via an interface (40, 42); ascertaining a measure (52, 56, 58) of the period duration of the clock signal (38) in the controller (28) based on the period duration of the clock signal (38); comparing the period duration with at least one period duration threshold value (46, 48); and providing a fault signal (50) when there is a deviation in a measure (52, 56, 58) of the period duration of the clock signal (38) from the period duration threshold.

2. The method according to claim 1, characterized in that two period duration threshold values (46, 48) are prespecified, and in that the fault signal (50) is provided when the measure (52, 56, 58) of the period duration exceeds an upper period duration threshold value (46) or falls below a lower period duration threshold value (48).

3. The method according to claim 1, characterized in that the quality signal (26) is transmitted via a SENT interface (40, 42).

4. The method according to claim 1, characterized in that the measure (52, 56, 58) for the period duration is ascertained from the duration (52) of a synchronization pulse (54) of the interface (40, 42).

5. The method according to claim 1, characterized in that the measure (52, 56, 58) of the period duration is ascertained from the time interval (56, 58) between two synchronization pulses (54) of the interface (40, 42).

6. The method according to claim 1, characterized in that the quality sensor (24) evaluates the propagation time of an ultrasound signal (30) which passes through the urea/water solution (14), and in that a measure of the propagation time is transmitted via the interface (40, 42).

7. A non-transitory machine-readable medium having a program code for diagnosing the quality signal (26) according to claim 1 when the program code is executed on the controller (28).

8. A controller (28) for diagnosing a quality sensor (24) which is used in a tank (12) of a reagent metering system (10), wherein the reagent metering system (10) meters a urea/water solution (14) stored in a tank (12) the quality of the urea/water solution (14) is checked by the quality sensor (24), upstream of an SCR catalytic converter (20), wherein the quality sensor (24) includes a signal-processor (34) having a clock generator (36) which provides a clock signal (38), wherein the quality sensor (24) ascertains the quality signal (26) on the basis of a time-based measurement, the controller (28) receiving the quality signal (26) via an interface (40, 42); ascertaining a measure (52, 56, 58) of the period duration of the clock signal (38); comparing the period duration with at least one period duration threshold value (46, 48); and providing a fault signal (50) when there is a deviation in a measure (52, 56, 58) of the period duration of the clock signal (38) from the period duration threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawing and explained in greater detail in the following description.

(2) The FIGURE shows a reagent metering system in which a method according to the invention for diagnosing a quality sensor which is used in the reagent metering system runs.

DETAILED DESCRIPTION

(3) The FIGURE shows a reagent metering system 10 which meters a urea/water solution 14, which is stored in a tank 12, into an exhaust gas duct 16 of an internal combustion engine 18 upstream of an SCR catalytic converter 20. The internal combustion engine 18 is provided, for example, as a drive motor in a motor vehicle. Ammonia (NH.sub.3), which serves as a reducing agent in the SCR catalytic converter 20 for reducing NO.sub.x components of the exhaust gas of the internal combustion engine 18, is produced in the exhaust gas duct 16 from the urea/water solution 14 at high temperature.

(4) The required metering rate of the urea/water solution 14 is preferably defined by means of a metering valve 22.

(5) A quality sensor 24, which ascertains a quality signal 26 and supplies the said quality signal to a control device 28, is provided for diagnosing the urea/water solution 14 to the correct concentration of the urea component.

(6) The urea/water solution 14 is subject to an ageing process in which the urea/water solution 14 decomposes, wherein ammonia is produced, so that the urea concentration is reduced. Furthermore, it is not possible to prevent the urea/water solution 14, when it is refilled, from being manipulated by, for example, the water content being increased. The urea concentration is also reduced in this case. However, at a reduced urea concentration of the urea/water solution 14, an excessively low effective metering rate is achieved at a prespecified metering rate by the metering valve 22, so that the NO.sub.x reduction in the SCR catalytic converter 20 no longer reaches the maximum possible values, as a result of which prespecified NO.sub.x concentrations downstream of the SCR catalytic converter 20 may possibly no longer be complied with. The urea concentration of the urea/water solution 14 should be approximately 32.5% by weight in line with the standard ISO 22241 or DIN 70070.

(7) The quality sensor 24 carries out a time-based measurement. A suitable method is, for example, an ultrasound measurement in which the signal propagation time of an ultrasound signal 30 is detected. For this purpose, the quality sensor 24 contains an ultrasound sensor 32 and a signal-processing arrangement 34 which contains a clock generator 36 which provides a clock signal 38. The ultrasound sensor is described in detail in laid-open specification DE 10 2015 212 622 A1 which was mentioned in the introductory part and to which reference is made.

(8) The clock signal 38 is supplied both to the ultrasound sensor 32 and also to a first interface 40.

(9) The first interface 40 provides the quality signal 26 which is transmitted to the control device 28 and is received there by a second interface 42. The transmission of the quality signal 26 is intended to be coupled to the time of the clock signal 38 which is provided by the clock generator 36. Transmission of this kind is possible, for example, via a serial interface, for example with the SENT protocol which was mentioned in the introductory part.

(10) The dependence of the quality signal 26, which is transmitted via the interface 40, 42, on the clock signal 38 allows the control device 28 to evaluate the clock signal 38 or the period duration of the clock signal 38.

(11) The FIGURE illustrates the time profile of the quality signal 26 as part of a serial data transmission operation, for example with the SENT protocol.

(12) The diagnosis according to the invention is based on ascertaining and evaluating a measure of the period duration or the frequency of the clock signal 38 in the control device 28 since, when there is a deviation in the period duration from a setpoint value, it is possible to conclude that there is not only a faulty clock signal 38 but rather, correspondingly, also a faulty time-based measurement by the quality sensor 24.

(13) The control device 28 contains a signal evaluation means 44 which is supplied with a first and a second period duration threshold value 46, 48 and which provides a fault signal 50 in the event of a fault.

(14) By way of example, the duration 52 of a synchronization pulse 54, for example of the SENT protocol, can be used as a measure 52, 56, 58 of the period duration of the clock signal 38. As an alternative or in addition, the time interval 56 between two immediately successive synchronization pulses 54, for example of the SENT protocol, can form the basis for the evaluation. As an alternative or in addition, a further time interval 58 between two synchronization pulses 54, for example of the SENT protocol, can form the basis for evaluating the measure of the period duration of the clock signal 38, wherein there are a large prespecified number of synchronization pulses 54 within the further time interval 58.

(15) The measure 52, 56, 58 of the period duration of the clock signal 38 can be compared with one or with two period duration threshold values 46, 48 in the signal evaluation means 44. The fault signal 50 is provided when the measure 52, 56, 58 of the period duration of the clock signal 38 is above the first period duration threshold value 46 or when the measure 52, 56, 58 for the period duration of the clock signal 38 is below the second period duration threshold value 48.

(16) The fault signal 50 can be processed and/or, for example, displayed in a further signal-processing arrangement. A fault signal 50 having occurred means that a deviation has occurred in the period duration of the clock signal 38 and that, as a result, a faulty quality signal 26 has been transmitted from the quality sensor 24 to the control device 28. When a fault signal 50 has occurred, it is necessary to check the quality sensor 24 which can be repaired or replaced. A possibly prescribed on-board diagnosis can be carried out by means of the fault signal 50.