Method for detecting a leaking point in a heat recovery system

Abstract

A method for detecting a leaking point in a heat recovery system of an internal combustion engine of a motor vehicle, wherein the heat recovery system includes a combustible working medium and a working medium circuit with an evaporator, a pump and an expansion machine. The recirculated exhaust gas of the engine flows through or around the evaporator which is arranged in an exhaust-gas return line. At least one oxidation catalytic converter is arranged in an exhaust gas line of the engine. A first temperature sensor is arranged in the exhaust gas line upstream and a second exhaust gas temperature sensor is arranged downstream of the oxidation catalytic converter. Temperatures of the exhaust gas are measured with these temperature sensors during operation of the engine in the exhaust gas line upstream and downstream of the oxidation catalytic converter. A temperature difference of the exhaust gas upstream and downstream of the oxidation catalyst is determined, wherein upon occurrence of an abnormally high temperature difference a conclusion is drawn on a leak in the evaporator.

Claims

1. A method for detecting a leaking point in a heat recovery system of an Internal combustion engine of a motor vehicle, wherein the heat recovery system comprises at least one combustible working medium and a working medium circuit with at least one exhaust gas recirculation (EGR) evaporator, a pump and at least one expansion machine, wherein the recirculated exhaust gas of the Internal combustion engine flows through or around the EGR evaporator which Is arranged in an exhaust-gas return line, and wherein at least one oxidation catalytic converter is arranged in an exhaust gas line of the Internal combustion engine, wherein a first temperature sensor is arranged in the exhaust gas line upstream of the oxidation catalytic converter and a second exhaust gas temperature sensor is arranged downstream of the oxidation catalytic converter, and temperatures of the exhaust gas are measured with the first and second temperature sensors during operation of the Internal combustion engine in the exhaust gas line upstream and downstream of the oxidation catalytic converter, and a temperature difference of the exhaust gas upstream and downstream of the oxidation catalyst is determined, wherein upon occurrence of at least an abnormally high temperature difference a conclusion is drawn on a leak in the EGR evaporator.

2. The method according to claim 1, wherein for at least one defined stationary operating mode of the Internal combustion engine, a maximum stationary setpoint value Is defined for the temperature difference upstream and downstream of the oxidation catalytic converter, wherein the internal combustion engine is operated in said stationary operating mode and the determined temperature difference is compared with the defined stationary setpoint value of the defined stationary operating mode, and wherein a conclusion is drawn on a leakage at the EGR evaporator when the determined temperature difference is greater than the maximum stationary temperature stationary setpoint value of the defined stationary operating mode.

3. The method according to claim 1, wherein a maximum transient setpoint value for the temperature difference upstream and downstream of the oxidation catalytic converter is defined for at least one defined transient operating mode of the internal combustion engine, wherein the Internal combustion engine is operated in the transient operating mode and the determined temperature difference is compared with the defined transient setpoint value of the defined transient operating mode, and wherein a conclusion is drawn on a leakage in the EGR evaporator when the determined temperature difference is greater than the maximum transient setpoint value of the defined transient operating mode.

4. The method according to claim 1, wherein a minimum value for a temporal reduction in the temperature difference upstream or downstream of the oxidation catalytic converter is defined for at least one defined, load-free operating mode of the internal combustion engine during idle running, coasting operation or motor-braking operation of the Internal combustion engine, wherein the Internal combustion engine is operated in this load-free operating mode and a temporal curve of the temperature difference upstream and downstream of the oxidation catalytic converter is determined and compared with the defined minimum value for the temporal reduction in the temperature difference, and wherein a conclusion is drawn on a leakage in the EGR evaporator when the reduction in the determined temporal curve of the temperature difference is lower than the minimum value for the temporal reduction in the temperature difference upstream and downstream of the oxidation catalyst in the load-free operating mode.

5. The method according to claim 1, wherein in normal engine operation of the Internal combustion engine upon the occurrence of an abnormally high temperature difference a plausibility check is carried out in that the injection quantity of fuel and it is examined whether a reduction in the measured temperature difference occurs after the expiration of a defined waiting time, and if an abnormally high temperature difference still detected upstream and downstream of the oxidation catalyst, a conclusion Is drawn on a leakage in the EGR evaporator.

6. The method according to claim 1, wherein injection of the fuel Is reduced or stopped in the motor-braking mode of the Internal combustion engine, and it Is examined whether a substantial reduction in the measured temperature difference occurs after expiration of a defined time period, and if an abnormally high temperature difference is still detected upstream and downstream of the oxidation catalyst, a conclusion Is drawn on a leakage in the EGR evaporator.

7. The method according to claim 1, wherein an abnormally high temperature difference is determined when the difference of the measured temperature is greater than 1020 downstream and upstream of the oxidation catalyst.

8. The method according to claim 7, wherein the waiting time is at least 30 to 60 seconds.

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

10. The method according to claim 1, wherein the conclusion Is drawn on the leak in the EGR evaporator after carrying out a plausibility check.

11. The method according to claim 4, wherein the load-free operating mode of the Internal combustion engine is selected from the group of Idle running operation, coasting operation or motor-braking operation of the Internal combustion engine.

12. The method according to claim 5, wherein the injection quantity of fuel is reduced or stopped by means of a closed control loop.

13. The method according to claim 6, wherein the time period Is at least 30 to 60 seconds.

14. An Internal combustion engine, comprising a heat recovery system which has at least one particularly combustible working medium and a working medium circuit with at least one exhaust gas recirculation (EGR) evaporator, a pump and at least one expansion machine, wherein the EGR evaporator is arranged in an exhaust gas recirculation line of the Internal combustion engine, and wherein at least one oxidation catalytic converter is arranged in at least one exhaust gas line of the Internal combustion engine, wherein a first temperature sensor is arranged upstream of the oxidation catalytic converter and a second temperature sensor is arranged downstream of the oxidation catalytic converter, and with said first and second temperature sensors, the temperature of the exhaust gas in the exhaust gas line of the internal combustion engine can be measured upstream and downstream of the oxidation catalytic converter, wherein said first and second temperature sensors are connected to at least one of an electronic control and evaluation unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The Invention will be explained in greater detail below with reference to a non-limiting exemplary embodiment shown in the drawings, wherein:

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

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

(4) FIGS. 2 and 3 show a temporal progression of the load and the determined temperature difference for a leakage-free heat recovery system, and

(5) FIGS. 4 and 5 show a temporal progression of the load and the determined temperature difference for a leakage-containing heat recovery system when using the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) FIGS. 1 and 2 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 return line 4. The exhaust gas return line 4 serves for external exhaust gas return between the exhaust system 22 and the intake system 23 of the internal combustion engine 1.

(7) An exhaust gas after-treatment device 5 is arranged in the exhaust gas line 3, which in the exemplary embodiment has a diesel oxidation catalytic converter 6, a diesel particle filter 7, an SCR catalytic converter 8 and a barrier catalytic converter 9. An NH.sub.3-containing additive can be fed via an injection device 10 upstream of the SCR catalytic converter 8. A mixer 11 serves for mixing and evaporation of the injected additive in the exhaust stream.

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

(9) Further, an EGR evaporator 14a (EGR=Exhaust Gas Recirculation) is provided in the exhaust gas recirculation line 4, which may be incorporated into the working medium circuit 13 of the heat recovery system 12 upstream or downstream of the evaporator 14. In the first embodiment variant shown in FIG. 1a, the second evaporator 14a is integrated into the working medium circuit 13 downstream of the first evaporator 14. Alternatively, however, the second evaporator 14a can also be arranged in a second working medium circuit 13a of the heat recovery system 12, which has a second pump 15a, a second expansion machine 16a and a second condenser 17a, as shown in FIG. 1b.

(10) A first temperature sensor 30 is arranged upstream of the oxidation catalytic converter 6 and a second temperature sensor 31 is arranged downstream of the oxidation catalytic converter 6. The temperature sensors 30, 31 are connected to a control and/or evaluation unit 21.

(11) With the first 30 and second temperature sensors 31, the exhaust gas temperatures T.sub.30 or T.sub.31 are measured in the exhaust gas line 3 upstream or downstream of the oxidation catalytic converter and a temperature difference T is determined on the oxidation catalytic converter 6 between its input 6a and the output 6b.

(12) In the oxidation catalytic converter 6, mainly unburnt hydrocarbons (C.sub.mH.sub.n) and carbon monoxide (CO) are converted to carbon dioxide and water. During this process, energy is released of the order of the lower calorific values of carbon monoxide and hydrocarbons. The lower calorific value of CO is approximately 10.1 MJ/kg, the lower calorific value of C.sub.mH.sub.n is, for example, 42 MJ/kg (equivalent to diesel/lubricating oil). During the conversion of the C.sub.mH.sub.n and the CO in the oxidation catalytic converter 6, the released energy is used to heat the oxidation catalytic converter 6 and to heat the exhaust gas stream passing through the oxidation catalytic converter 6.

(13) The increase in the exhaust gas temperature during the through-flow of the oxidation catalytic converter 6 is dependent on the concentration of the hydrocarbons and the carbon monoxide at the inlet of the oxidation catalytic converter 6.

(14) If leakage occurs in the region of the EGR evaporator 14a, this results in an increased temperature difference T between the temperature T.sub.31 at the output 6b and the temperature T.sub.30 at the input 6a of the oxidation catalytic converter 6.

(15) When an abnormally high temperature difference T between the measured values of the second temperature sensor 31 and the first temperature sensor 30 occurs during the normal engine operation of the internal combustion engine 1, this temperature difference T is subjected to a plausibility check by reducing or stopping the injection quantity of fuel through the fuel injection devices (not shown in closer detail) into the internal combustion engine 1 by using a closed control circuit for example, and it is examined whether a substantial reduction in the measured temperature difference occurs after a defined first waiting time (for example 30 to 60 seconds) has elapsed. Furthermore, if an abnormally high temperature difference T is still detected, a conclusion can be drawn on a leakage in the EGR evaporator 14a.

(16) Alternatively or additionally, the injection of the fuel can be reduced or stopped for carrying out a plausibility check in the motor-braking mode of the internal combustion engine 1, and it can be examined whether a substantial reduction in the measured temperature difference T occurs after a defined second waiting time has elapsed, and if an abnormally high temperature difference T is still determined upstream and downstream of the oxidation catalytic converter 6, a conclusion can be drawn on a leakage in the EGR evaporator 14a.

(17) The method according to the invention can be carried out during a stationary operating mode, a transient operating mode or a load-free operating mode of the internal combustion engine 1.

(18) In order to carry out a leakage test in stationary operation, a maximum stationary setpoint value for the temperature difference T upstream and downstream of the oxidation catalytic converter 6 is defined for at least one defined stationary operating mode of the internal combustion engine 1. The internal combustion engine 1 is operated in this stationary operating mode and the determined temperature difference T is compared with the defined stationary setpoint value of the defined stationary operating mode. If the determined temperature difference T is greater than the maximum stationary setpoint value of the defined stationary operating mode, a conclusion can be drawn on a leakage in the EGR evaporator 14a.

(19) In order to carry out the leakage test in transient operation, a maximum transient setpoint value for the temperature difference T upstream and downstream of the oxidation catalytic converter 6 is defined for at least a defined transient operating mode of the internal combustion engine 1. The internal combustion engine 1 is operated in this transient operating mode and the determined temperature difference T is compared with the defined transient setpoint value of the defined transient operating mode. A conclusion is drawn on a leakage in the evaporator if the determined temperature difference T is greater than the maximum transient setpoint value of the defined transient operating mode.

(20) The leakage test can also be carried out during at least one load-free operating mode of the internal combustion engine 1, e.g. idling running, coasting operation or motor-braking operation. A minimum value for the temporal reduction of the temperature difference T upstream and downstream of the oxidation catalytic converter 6 is defined for at least a defined load-free operating mode of the internal combustion engine 1. The internal combustion engine 1 is operated in this load-free operating mode and a temporal progression of the temperature difference T upstream and downstream of the oxidation catalytic converter 6 is determined and compared with the defined minimum value for the temporal reduction in the temperature difference T. If the reduction in the determined temporal progression of the temperature difference T is less than the minimum value for the temporal reduction of the temperature difference T upstream and downstream of the oxidation catalytic converter 6 in the load-free operating mode, a conclusion can be drawn on a leakage in the EGR evaporator 14a.

(21) FIGS. 2 and 3 show a temporal progression of the load L and the temperature difference T for a leakage-free heat recovery system 12 during a changeover of the internal combustion engine 1 to the motor-braking mode. Usually, the injection of the fuel is substantially reduced or stopped during the motor-braking operation. It can clearly be seen that the determined temperature difference T drastically decreases, thus there is no leakage.

(22) FIGS. 4 and 5, on the other hand, show a changeover to motor-braking operation when there is a leakage in the EGR evaporator 14a. In this case, there is no reduction in the temperature difference T. On the contrary, due to the unchanged leakage and the lower gas throughput of the exhaust gas return line in the motor-braking operation, an increase in the temperature difference T can even occur, as shown by the dashed line curve a). The line b) shows the case that no change occurs in the temperature difference T. Furthermore, it can happen that the reduction in the temperature difference T is substantially lower than expected, i.e. the minimum value indicated by line d) for the temporal reduction of the temperature difference T is not reached. In these cases a), b), c), a leakage of the EGR evaporator 14a can be clearly concluded and a corresponding leakage warning can be output to the driver.

(23) The main advantage of the present invention is that no additional complex leakage detectors have to be installed. In the ideal case, first 30 and second temperature sensors 31 arranged as a standard in the exhaust gas line 3 can be used in order to enable reliable leakage tests to be carried out.