Method for detecting an unsealed location in a heat recovery system

Abstract

The invention relates to a method for detecting an unsealed location in a heat recovery system of an internal combustion engine of a motor vehicle. The heat recovery system has at least one working medium, in particular a combustible working medium, and a working medium circuit with at least one evaporator, a pump, and at least one expansion machine to allow an early and reliable detection of leakages in the evaporator.

Claims

1. A method for detecting a leak in a heat recovery system of an internal combustion engine of a motor vehicle, wherein the heat recovery system comprises: at least one particularly combustible working medium; a working medium circuit having at least one evaporator, arranged in an exhaust gas flow path of the internal combustion engine; a pump; at least one expansion machine; wherein at least one NH.sub.3 sensor is arranged downstream of the at least one evaporator in the exhaust gas flow path, and configured to measure the exhaust gas, and wherein after the occurrence of at least one abnormally high NH.sub.3 measured value a conclusion is drawn on a leakage of the evaporator.

2. The method according to claim 1, wherein a chemical substance serves as a working medium to which the NH.sub.3 sensor reacts.

3. The method according to claim 1, wherein a plausibility check is carried out in the engine operation of the internal combustion engine when an abnormally high NH.sub.3 measured value is detected, in that the injection quantity of an NH.sub.3-containing additive is reduced or stopped upstream of the SCR storage catalytic converter, and checking whether after the expiration of a defined first waiting time, a substantial reduction in the measured NH.sub.3 concentration occurs, and if an abnormally high NH.sub.3 measured value is still detected, a conclusion is drawn on a leakage of the evaporator.

4. The method according to claim 1, wherein the injection of an NH.sub.3-containing additive upstream of the SCR storage catalytic converter is reduced or stopped during the motor-braking operation of the internal combustion engine, and it is examined whether, after the expiration of a defined second waiting period, a substantial reduction in the measured NH.sub.3 concentration occurs, and if an abnormally high NH.sub.3 measured value is still detected, a conclusion is drawn on a leakage of the evaporator.

5. The method according to claim 1, wherein an abnormally high NH.sub.3 measured value is determined when the average NH.sub.3 measured value is above 10 ppm.

6. The method according to claim 1, wherein the first and/or second waiting time is at least 30 to 60 seconds.

7. The method according to claim 1, wherein a corresponding warning signal is output when a leakage of the evaporator is detected.

8. The method according to claim 1, wherein a plausibility check is carried out on the measured value before the conclusion is drawn on the leakage of the evaporator.

9. The method according to claim 2, wherein the NH.sub.3 sensor has a cross-sensitivity to said chemical substance.

10. The method according to claim 3, wherein the injection quantity of an NH.sub.3-containing additive is reduced or stopped upstream of the SCR storage catalytic converter by using a closed control loop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in detail below using a non-restrictive embodiment example shown in the drawings, wherein:

(2) FIG. 1a schematically shows an internal combustion engine according to the invention in a first embodiment variant;

(3) FIG. 1b schematically shows an internal combustion engine according to the invention in a second embodiment variant;

(4) FIG. 2 and FIG. 3 show a time curve of the load and the NH.sub.3 measured values for a leakage-free heat recovery system; and

(5) FIG. 4 and FIG. 5 show a time curve of the load and the NH.sub.3 measured values for a leaky heat recovery system when applying the present invention.

DETAILED DESCRIPTION

(6) FIG. 1a and FIG. 1b each show an internal combustion engine 1 with exhaust gas flow paths 2, which are formed by an exhaust gas line 3 and an exhaust gas recirculation line 4. The exhaust gas recirculation line 4 is used for external exhaust gas recirculation between exhaust system 22 and intake system 23 of the combustion engine 1.

(7) An exhaust aftertreatment device 5 is arranged in the exhaust gas line 3, which has a diesel oxidation catalytic converter 6, a diesel particulate filter 7, an SCR catalytic converter 8 and a barrier catalytic converter 9 in the embodiment example. An NH.sub.3-containing additive can be fed upstream of the SCR catalyst 8 via an injection device 10. A mixer 11 is used to mix and evaporate the injected additive in the exhaust gas stream.

(8) A heat recovery system 12 with a closed working medium circuit 13 for a working medium, for example ethanol, which has at least one first evaporator 14, a pump 15 and at least one expansion machine 16, is provided for recovering the exhaust gas waste heat. Reference numeral 17 denotes a condenser. To bypass the first evaporator 14 on the exhaust side, a bypass line 18 is provided, which branches off from the exhaust gas line 3 upstream of the first evaporator 14 and flows back into the exhaust gas line 3 downstream of the first evaporator 14. Reference numeral 19 denotes a control element formed, for example, by a changeover flap for switching the exhaust gas flow between the flow path through the first evaporator 14 and the bypass line 18.

(9) Optionally, a second evaporator 14a may be provided in the exhaust gas recirculation line 4, which may be integrated upstream or downstream of the first evaporator 14 into the working medium circuit 13 of the heat recovery system 12.

(10) In the first embodiment variant shown in FIG. 1a, the second evaporator 14a is integrated downstream of the first evaporator 14 into the working medium circuit 13. Alternatively, the second evaporator 14a can also be arranged in a second working medium circuit 13a of the heat recovery system 12 comprising a second pump 15a, a second expansion machine 16a and a second condenser 17a, as shown in FIG. 1b.

(11) Downstream of the first evaporator 14, an NH.sub.3 sensor 20 is arranged in the exhaust gas line 3. Another NH.sub.3 sensor 20a may be located downstream of the second evaporator 20a in the exhaust gas recirculation line 4. The NH.sub.3 sensors 20, 20a are connected to a control and/or evaluation unit 21.

(12) The NH.sub.3 sensors 20, 20a each have a cross-sensitivity to the working mediumin this case to ethanolor to a component of the working medium. This means that the NH.sub.3 sensors not only detect NH.sub.3 measured values from ammonia actually contained in the exhaust gas, but also from the substance initiating the cross-sensitivity. If there is a leakage in the area of evaporator 14 or 14a, this is reflected in the output increased NH.sub.3 measured values of the NH.sub.3 sensors 20 or 20a.

(13) If an abnormally high NH.sub.3 measured value of the first NH.sub.3 sensor 20 occurs during normal engine operation of internal combustion engine 1, this NH.sub.3 measurement value is subjected to a plausibility check, in that the injection quantity of the NH.sub.3-containing additive is reduced or stopped by the injection device 10 upstream of the SCR storage catalyst 8for example using a closed control loopby means of the injection device 10, and it is investigated whether a substantial reduction in the measured NH.sub.3 concentration occurs after a defined first waiting time (for example 30 to 60 seconds) has elapsed. If an abnormally high NH.sub.3 reading continues to be detected, a leakage at the first evaporator 14 may be concluded.

(14) As an alternative to engine operation, the method according to the invention for detecting an unsealed location in the heat recovery system 12 can also be carried out during motor-braking operation or when switching from engine operation to motor-braking operation. During motor-braking operation of internal combustion engine 1, the injection of an NH.sub.3-containing additive upstream of the SCR storage catalyst 8 is stopped and it is investigated whether a significant reduction in the measured NH.sub.3 concentration occurs after a defined second waiting time of 30 to 60 seconds, for example. If there is no significant reduction in the NH.sub.3 measured value, a leakage at the first evaporator 14 can be concluded. If it cannot be ruled out that a working medium possibly escaping from the second evaporator 14a is eliminated or chemically modified in the internal combustion engine 1 or in the exhaust aftertreatment system 5, it is advantageous to use a second NH.sub.3 sensor 20a directly downstream of the second evaporator 14a in the exhaust gas recirculation line 4, via which leakages of the second evaporator 14a can be detected directly.

(15) FIG. 2 and FIG. 3 show a time curve of the load L and the NH.sub.3 measured values for a leakage-free heat recovery system 12 during a changeover of the internal combustion engine 1 to motor-braking operation. Usually the injection of the NH.sub.3 additive is stopped during motor-braking operation. It can clearly be seen that the measured NH.sub.3 measured value of the first NH.sub.3 sensor 20 decreases drasticallythere is therefore no leakage.

(16) FIG. 4 and FIG. 5, on the other hand, show a changeover to motor-braking operation if there is a leakage in the first evaporator 14. In this case there is no reduction in the NH.sub.3 measured value. On the contrarydue to the unchanged leakage and the lower gas throughput due to the exhaust gas path in motor-braking operation, there may even be an increase in the NH.sub.3 measured value, as the dashed line shows. In this case, a leakage of the evaporator 14 can be clearly identified and a corresponding leakage warning can be issued to the driver.

(17) The main advantage of this invention is that it does not require the use of overly complex leakage detectors. Ideally, an NH.sub.3 sensor 14 already fitted as standard in the exhaust gas linealbeit at a point downstream of the evaporator in the exhaust gas flow path 2can be used to carry out reliable leakage tests.