Method and Device for Predicting and Avoiding Condensation of Humidity in an Intake System of an Internal Combustion Engine After Engine Switch Off

Abstract

The present invention relates to a method and a control unit for avoiding condensation of humidity in an intake system of an internal combustion engine after engine switch off. Condensed liquid in the intake system of the stopped engine can lead to icing, corrosion and a hydrostatic lock at the next engine start. To prevent such an engine damage, it is necessary to determine if and in which amount condensed liquid occurs in the cooled intake system and to initiate appropriate actions to eliminate the liquid therefrom. The present invention predicts the occurrence of condensation in the intake system of the cooled engine and initiates corrective measures at engine switch off and during the cooling down period.

Claims

1. Method for avoiding condensation of humidity in an intake system of an internal combustion engine, the method determining a liquid mass (m.sub.H2O, m.sub.H2O) condensing in the intake system at least one predetermined timing after engine switch off request, based on a determined humidity (h.sub.intake) in the intake system, a determined temperature (T.sub.intake) in the intake system and a determined ambient temperature (T.sub.ambient); and initiating a corrective measure if the determined condensed liquid mass (m.sub.H2Op, m.sub.H2O) exceeds a predetermined threshold (m.sub.TH1, m.sub.TH2).

2. Method according to claim 1, wherein the prediction of the condensed liquid mass (m.sub.H2Op) comprises the steps of: measuring the relative humidity (h.sub.intake) and the temperature (T.sub.intake) in the intake system and calculating a first humidity ratio in the intake system based on the measured values, estimating a liquid mass stored as film on walls of the intake system, calculating a second humidity ratio in the intake system including the liquid wall film mass and the first humidity ratio, measuring the ambient temperature (T.sub.ambient) and estimating a cooling down period until the intake air cools down to ambient temperature (T.sub.ambient), and calculating the condensed liquid mass depending on the second humidity ratio and an estimated soaking temperature (T.sub.soak) at end of the cooling down period (t.sub.e).

3. Method according to claim 2, wherein, if the predicted condensed liquid mass exceeds a first predetermined threshold (m.sub.TH1) and the estimated soaking temperature (T.sub.soak) at the end of the cooling down period (t.sub.e) is higher than a first predetermined temperature (T.sub.TH1), a first corrective measure as the corrective measure is initiated after engine switch off request.

4. Method according to claim 3, wherein, to perform the first corrective measure, a control unit initiates a predetermined number of cranking cycles after engine switch off request.

5. Method according to claim 3, wherein, if the predicted condensed liquid mass (m.sub.H2Op) exceeds a second predetermined threshold (m.sub.TH2) smaller than the first predetermined threshold (m.sub.TH1), and the estimated soaking temperature (T.sub.soak) at the end of the cooling down period (t.sub.e) is lower than the first predetermined temperature (T.sub.TH1), a second corrective measure as the corrective measure is initiated after engine switch off request.

6. Method according to claim 5, wherein, to perform the second corrective measure, the control unit initiates a predetermined number of scavenging cycles after engine switch off request by switching an intake valve and an exhaust valve in a valve overlap position and controlling an e-booster to provide a predetermined boost pressure.

7. Method according to claim 1, wherein the humidity (h.sub.intake) in the intake system, the temperature (T.sub.intake) in the intake system and the ambient temperature (T.sub.ambient) are frequently measured at predetermined timings during the cooling down period after engine switch off until the temperature in the intake system is equal to the ambient temperature (T.sub.ambient) and the condensed liquid mass (m.sub.H2O) is determined based on the measured values at each timing.

8. Method according to claim 3, wherein, if the determined condensed liquid mass (m.sub.H2O) exceeds the first predetermined threshold (m.sub.TH1), and the measured ambient temperature (T.sub.ambient) is higher than a second predetermined temperature (T.sub.TH2), a third corrective measure as the corrective measure is initiated.

9. Method according to claim 8, wherein, to perform the third corrective measure, the control unit switches the intake valve and the exhaust valve in the valve overlap position and/or opens a venting valve and controls the e-booster to deliver a first predetermined air mass flow for a first predetermined ventilation time.

10. Method according to claim 8, wherein, if the determined condensed liquid mass (m.sub.H2O) exceeds a second predetermined threshold (m.sub.TH2), and the measured ambient temperature is lower than the second predetermined temperature (T.sub.TH2), a fourth corrective measure as the corrective measure is initiated.

11. Method according to claim 10, wherein, to perform the fourth corrective measure, the control unit switches the intake valve and the exhaust valve in a valve overlap position and/or opens the venting valve and controls the e-booster to deliver a second predetermined air mass flow for a second predetermined ventilation time.

12. Control unit for an internal combustion engine having at least one cylinder, at least one intake valve, at least one exhaust valve, at least one e-booster, at least one venting valve, at least one humidity sensor, at least one temperature sensor and at least one non-combustible fluid injector for injecting non-combustible fluid in at least one intake port of the internal combustion engine, the control unit configured to perform the method according to claim 1.

13. Internal combustion engine including the control unit of claim 12.

14. A computer program product storable in a memory comprising instructions which, when carried out by a computer, cause the computer to perform the method according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 depicts a schematical diagram of a turbocharged three-cylinder engine;

[0029] FIG. 2 shows schematically a cylinder of an internal combustion engine, wherein the gas exchange valves are switched into a valve overlapping position;

[0030] FIG. 3 depicts schematically an exemplary water amount in the intake system which should not be exceeded to avoid that the throttle plate is blocked in case of icing;

[0031] FIG. 4 shows schematically an exemplary water amount in the cylinder which should not be exceeded to avoid an engine damage by a hydrostatic lock;

[0032] FIG. 5 (5a and 5b) shows diagrams which exemplary illustrate the formation of condensed water after switching off the engine;

[0033] FIG. 6 depicts a flow chart which describes an example for predicting and preventing condensed water in the cooled engine at engine switch off;

[0034] FIG. 7 depicts a flow chart which describes an example for determining and preventing condensed water during the cooling down period of the engine.

DESCRIPTION OF EMBODIMENTS

[0035] In FIG. 1 a three-cylinder turbocharged engine is schematically illustrated. The number of cylinders is not limited to three but may be any number of cylinders as known. The engine comprises a turbocharger 2, having a compressor 2a and a turbine 2b, an electrical booster (e-booster) 4, a first bypass plate 3 to bypass the e-booster 4, a charge air cooler 5, a second bypass plate 6 to bypass the charge air cooler 5, a throttle plate 7 mounted at an intake manifold 10, which is equipped with a humidity sensor 8, an intake temperature sensor 9 and a venting valve 11. The humidity sensor 8, the temperature sensor 9 and the venting valve 11 may also be mounted at any other representative position in the intake system. Further the engine includes intake ports 12-1 to 12-3, each connecting the intake manifold 10 with a respective cylinder 1-1 to 1-3, in order to draw fresh charge into each cylinder 1-1 to 1-3. In each intake port 12-1 to 12-3 a non-combustible fluid injector 13-1 to 13-3 is disposed, which is connected to the inside of the respective intake port and configured to inject non-combustible fluid into the intake port. The non-combustible fluid may preferably be water. To discharge the exhaust gases, each cylinder 1-1 to 1-3 is connected to an exhaust port 14-1 to 14-3 from which the exhaust gases are led to the turbine 2b of the turbocharger 2 in order to propel the compressor 2a before leaving the exhaust system of the engine.

[0036] Further, the engine comprises a at least one control unit 15 which may control the turbocharger 2, the e-booster 4, the bypass plates 3, 6, the throttle plate 7, the venting valve 11, the gas exchange valves (not depicted in FIG. 1) and the water injectors 13-1 to 13-3. Furthermore, the control unit 15 may receive signals from an ambient temperature sensor (not depicted), the intake humidity sensor 8 and the intake temperature sensor 9 to determine/predict the amount of condensed water when the engine is cooled down and during the cooling down period, respectively. The number and type of actuators and sensors is not limited to the depicted example.

[0037] The at least one control unit 15 may be integrated into the internal combustion engine or, alternatively, it may be disposed at a position within a vehicle remote to the combustion engine, and the control unit 15 and the engine may be connected via one or more signal lines. The control unit 15 may be the engine control unit (ECU) or a separate control device. There may also be a plurality of control units 15-1 to 15-x which may control subgroups of the controlled actuators, e.g. one control unit 15-1 may control only the water injectors, another control unit 15-2 may control only the charging and so on.

[0038] During steady state engine operation, fresh air may be conducted via the compressor 2a, the first bypass plate 3 and the charge air cooler 5 to the throttle plate 7 which may adjust the required amount of air for the combustion in the cylinders 1-1 to 1-3. In order to guide the air through the charge air cooler 5, the second bypass plate 6 has to be closed. At low engine temperature and/or load it may be beneficial to bypass the charge air cooler 5 by opening the second bypass plate 6.

[0039] During a transient engine operation mode, which requires a fast increase of engine power, the incoming air may be conducted via the compressor 2a to the e-booster 4 by closing the first bypass plate 3. In this case the throttle plate 7 may be fully opened, and the air may be pushed into the cylinders 1-1 to 1-3 at an increased pressure level to enable the required power output of the engine. To ensure sufficient cooling of the high compressed air, the second bypass plate 6 may also be closed, so that the air may be directed through the charge air cooler 5.

[0040] In order to avoid knocking and high exhaust gas temperatures, water injection can be performed during transient operation mode and/or at high engine load and speed. For this purpose, water may be injected by the water injectors 13-1 to 13-3 into the intake ports 12-1 to 12-3 from which it is can enter into the cylinders 1-1 to 1-3 to decrease the combustion temperature therein. Since water injection into the intake ports 12-1 to 12-3 leads to a wall film therein, an amount of injected water may remain in the intake system when the engine is switched off. Therefore, the use of port water injection may increase the risk of an engine damage caused by water occurring in the intake system.

[0041] In FIG. 2 a schematic view of an exemplary cylinder 1 of an internal combustion engine is depicted. During an intake stroke of the engine when a piston 18 inside the cylinder 1 moves downward, fresh load can enter into the cylinder 1 from the intake port 12 through an intake valve 16. After a combustion has taken place in a working stroke of the engine, exhaust gases can be discharged by the upward movement of the piston 18 through an exhaust valve 17 into the exhaust port 14 during an exhaust stroke of the engine.

[0042] During a cranking cycle of the engine no combustion takes place, so that only air is pumped through the engine. To perform the first corrective measure to avoid condensed water in the intake system of the cooled engine, one or more cranking cycles may be performed during the shut down of the engine. For this purpose, both bypass plates 3, 6 and the throttle plate 7 may be fully opened to allow for an undisturbed inflow of dry fresh air into the engine.

[0043] For performing the second corrective measure, the air flow through the engine during the cranking cycles may be supported by the e-booster 4 which may provide a boost pressure in the intake port 12 being above the pressure in the exhaust port 14. In this case the first bypass plate 3 may be closed and the second bypass plate 6 as well as the throttle plate 7 may be fully opened. Additionally, the intake valve 16 and the exhaust valve 17 may be switched into a valve overlap position, so that both valves are open to bypass the cylinder 1 (see doted arrow in FIG. 2) which allows for an effective scavenging of the intake system.

[0044] For performing the third and fourth corrective measure at the stopped engine during the engine cool down period, scavenging air can only be delivered by the e-booster 4. Similar to the second corrective measure the first bypass plate 3 may be closed and the second bypass plate 6 as well as the throttle plate 7 may be fully opened. Further, the intake valve 16 and the exhaust valve 17 may be switched into a valve overlap position, so that both valves of at least one cylinder 1-1 to 1-3 are open to push the humid air out of the engine. Alternatively or in addition, the venting valve 11 in the intake manifold 10 may be opened to allow for escaping of humid air out of the intake system.

[0045] In FIG. 3 a first amount of condensed water 20 is illustrated as an example for determining the first predetermined threshold m.sub.TH1 of condensed liquid mass in order to prevent an engine damage in case the temperature in the intake system is above the freezing point. Liquid water entering into the cylinder during a shutdown period of the engine or at engine start can lead to a hydrostatic lock. Therefore, as an example, the amount of condensed water in the intake system should be lower than the amount of liquid 20 which would fill the distance C.sub.P between the piston 18 and the fire deck 19.

[0046] FIG. 4 depicts schematically a lateral and a plan view of the throttle plate 7 mounted in an intake pipe 21 to illustrate an example for determining the second predetermined threshold m.sub.TH2 of condensed liquid mass in the intake system which may be still permissible in case of icing. Between the outer diameter D.sub.TP of the throttle plate 7 and the inner diameter D.sub.IP of the intake pipe 21 there is a crevice C.sub.TP necessary to allow smooth movement of the throttle plate 7. Water which may condense in the range of the throttle plate 7 can accumulate on the lower side of the intake pipe 21. Therefore, the second amount of condensed water 22 accumulating on the lower side of the intake pipe 21 in the setting range L.sub.TP of the throttle plate 7 should not exceed a high which is larger than the clearance of the crevice C.sub.TP, in order to avoid blocking of the throttle plate 7 in case of icing,

[0047] FIG. 5a shows schematically an exemplary diagram for determining the formation of condensed water in the intake system by using a psychrometric chart. Point 1 marked in the diagram indicates an example for conditions in the intake system at engine switch off. According to the diagram, the intake temperature is 30° C. and the relative intake humidity is 40% at that time. At point 2 marked in the diagram the relative intake humidity is increased to 60% wherein the intake temperature has only slightly decreased. The increased relative humidity may be caused by vaporization of the wall film accumulated on the intake port walls and mixing of the vaporized water with the air in the intake system. In the following step the intake temperature drops off continually until at point 3 the saturation temperature of 20° C. is reached. At that point water condensation in the intake system starts and, in the following, persists until the engine is completely cooled down to ambient temperature. The ambient temperature in the present example is marked as 0° C. at point 4 in the diagram, so that the condensed amount of water can be determined based on the difference of the humidity ratio at 20° C. and 0° C.

[0048] FIG. 5b shows schematically the example of the four characteristic points during the cooling down period corresponding to FIG. 5a in a time-based presentation. In the presented diagram the progress of the intake temperature, the progress of the relative intake humidity and the progress of the condensed water mass are depicted. Again, point 1 represents exemplary conditions at engine switch off at which the air in the intake system has a relative humidity of 40% and a temperature of 30° C. At point 2 a certain time has passed in which the relative humidity has been increased to 60% due to the vaporization of the water wall film. Point 3 indicates the dew point at which water condensation starts and, in the following, the condensed water mass continuously increases until, at point 4, the engine is cooled down to the ambient temperature of 0° C. Since icing in the intake system can occur at that temperature, the condensed water mass should stay below the second threshold m.sub.TH2 as depicted, in order to prevent engine damage caused by blocking actuators such as a blocking throttle plate 7.

[0049] FIG. 6 depicts a flow chart which exemplary describes as to how to predict and prevent condensed water in the intake system of an internal combustion engine when the engine has cooled down. When engine switch off is requested, the intake humidity h.sub.intake, the intake temperature T.sub.intake and the ambient temperature T.sub.ambient are measured by the related sensors (S100) and the respective values are sent to the control unit 15. Then, in step S101, the control unit 15 estimates the wall film mass, for example, based on the measured conditions in the intake system and the amount of water injected into the intake ports 12-1 to 12-3 in the preceding cycle(s) before the engine switch off request, and calculates the humidity ratio after vaporization of the wall film according to the psychrometric chart as exemplary depicted in FIG. 5a (S102). Further, in step 5103, the control unit 15 predicts the soaking temperature T.sub.soak of the air inside the intake system at the end of the engine cool down period t.sub.e, wherein the soaking temperature may be achieved when the temperature T.sub.intake inside the intake system is identical to the ambient temperature T.sub.ambient. For this purpose, the control unit 15 may firstly calculate the time for cooling down the air in the intake system based on the currently determined conditions, for example, the intake temperature T.sub.intake and the currently measured ambient temperature T.sub.ambient. Subsequently, the predicted ambient temperature at the calculated end of the cooling down period may be estimated, for example, based on whether reports, which can be received via the internet from the next available whether station. If the forecasted ambient temperature strongly differs from the currently measured ambient temperature T.sub.ambient, some iteration steps may be necessary to predict the end of the engine cool down period t.sub.e and the soaking temperature T.sub.soak with sufficient accuracy. Further information measured by additional engine sensors, for example the coolant temperature of the engine, may be used for improving the accuracy of the calculation. Depending on the calculated humidity ratio and the predicted soaking temperature T.sub.soak, the control unit 15 can calculate the condensed water mass at the end of the engine cool down period t.sub.e (S104) according to the psychrometric chart as exemplary depicted in FIG. 5a.

[0050] If condensation is predicted at a soaking temperature T.sub.soak higher than a first temperature threshold T.sub.TH1, and the predicted condensed water mass m.sub.H2Op in the intake system may be larger than the first predetermined threshold m.sub.TH1, the first corrective measure is performed (S105), for example, one or more cranking cycles during engine switch off to fill the intake system with dry fresh air. The first temperature threshold T.sub.TH1 should be set around the freezing point, preferably in a temperature range of 0° C. to 5° C.

[0051] If condensation is predicted at a soaking temperature T.sub.soak lower than the first temperature threshold T.sub.TH1 and the predicted condensed water mass m.sub.H2Op in the intake system may be larger than the second predetermined threshold m.sub.TH2, the second corrective measure is performed (S106), for example, a scavenging cycle during engine switch off in order to push the humid air out of the intake system.

[0052] When the engine is fully stopped after finishing the explained calculations and performing the required measures, the conditions in the intake system (h.sub.intake, T.sub.intake) may be measured again and water condensation therein may be further monitored during the engine cool down period as described in FIG. 7.

[0053] FIG. 7 depicts a flow chart which describes by way of example as to how to determine and prevent condensed water during the cooling down period of the engine. At a predetermined time t.sub.1 after engine switch off the control unit 15 checks if the battery voltage is above a minimum level. The predetermined time t.sub.1 may be in a range of 1 s to 20 min and the minimum battery voltage level may be in a range of 7V to 9V. If the battery voltage is above the minimum level, intake humidity h.sub.intake, intake temperature T.sub.intake and ambient temperature T.sub.ambient are measured (S200). As long as the intake temperature T.sub.intake is higher than the ambient temperature T.sub.ambient, the control unit 15 determines whether and in which amount condensed water can occur in the intake system at the measured ambient temperature T.sub.ambient (S201).

[0054] If condensed water is determined at an ambient temperature T.sub.ambient higher than a second temperature threshold T.sub.TH2, and the determined water mass m.sub.H2O in the intake system is larger than the first predetermined threshold m.sub.TH1, the third corrective measure is performed (S203), for example, controlling the e-booster 4 to deliver a first predetermined air mass flow for a first predetermined ventilation time during which the intake valve 16 and the exhaust valve 17 are switched in valve overlap position and/or the venting valve 11 is opened. The second temperature threshold T.sub.TH2 should preferably be set in a temperature range of 10° C. to 15° C. in order to reliably avoid freezing of condensed water during the cool down period of the engine.

[0055] If condensed water is determined at an ambient temperature T.sub.ambient lower than the temperature threshold T.sub.TH2, and the determined water mass m.sub.H2O in the intake system is larger than the second predetermined threshold m.sub.TH2, the fourth corrective measure is performed (S204), for example, controlling the e-booster 4 to deliver a second predetermined air mass flow for a second predetermined ventilation time during which the intake valve 16 and the exhaust valve 17 are switched in valve overlap position and/or the venting valve 11 is opened.

[0056] The above described calculations and corrective measures can be performed repeatedly in predetermined time steps t.sub.1 as long as the battery voltage u.sub.bat stays above the minimum level u.sub.min. The procedure may be finished when the intake temperature T.sub.intake has reached the ambient temperature T.sub.ambient.

[0057] Instead of determining water condensation during the cool down period or in addition thereto, the previously predicted mass of condensed water m.sub.H2Op at the end of the cool down period t.sub.e may be adapted by currently measured boundary conditions (h.sub.intake, T.sub.intake, T.sub.ambient). Especially if no condensation is predicted and no corrective measure has been carried out during the engine shut down, it may be advantageous to double check the prediction during the cool down period. In this case, the third or fourth corrective measure may be performed even before water condensation occurs and therefore engine damage may be prevented effectively.

[0058] Features of the different embodiments, aspects and examples, which are described herein and which are shown by the Figures, may be combined either in part or in whole. The herein described invention shall also entail these combinations.

[0059] Again summarizing, the present subject-matter offers a method and a control unit 15 to determine and prevent condensed liquid in the intake system of a stopped engine. The control unit 15 determines if and in which amount condensed liquid occurs in the cooled intake system and initiates appropriate actions to eliminate the liquid therefrom. Hence, engine damages caused by water condensation can be prevented with high reliability.

REFERENCE SIGNS LIST

[0060] 1, 1-1, 1-2, 1-3: cylinder, 2: turbo charger, 2a: compressor, 2b: turbine, 3: first bypass plate, 4: electrical booster, e-booster, 5: charge air cooler, 6: second bypass plate, 7: throttle plate, 8: intake humidity sensor, 9: intake temperature sensor, 10: intake manifold, 11: venting valve, 12, 12-1, 12-2, 12-3: intake port, 13-1, 13-2, 13-3: water injector, 14, 14-1, 14-2, 14-3: exhaust port, 15: control unit, 16: intake valve, 17: exhaust valve, 18: piston, 19: fire deck, 20: first amount of condensed water, 21: intake pipe, and 22: second amount of condensed water.