Procedure for an engine

Abstract

Method for an engine (10), comprising: Increasing exhaust gas recirculation (EGR) flow in response to condensation in an EGR cooler (146, 158), characterized in that the condensation is an estimated amount of accumulated condensate, the estimated amount of accumulated condensate being based on an amount of condensate formed within the EGR cooler (146, 158) over a predetermined period of time and an amount of condensate evaporated within the EGR cooler (146, 158) over the predetermined period of time.

Description

AREA

[0001] The present disclosure relates to internal combustion engines. GENERAL STATE OF THE ART AND SUMMARY

[0002] Engine heat exchangers such as intercoolers and other coolers can operate to cool the charge air entering the intake manifold, providing higher-density charge air for increased engine power and improved fuel efficiency. Furthermore, the cooled charge air can reduce combustion temperatures and assist in the control of certain engine emissions. Under certain conditions, such as when the air in the heat exchanger is cooled below its dew point, condensate can form within the heat exchanger. This condensate can accumulate and then seep into the engine, causing misfiring and other problems; it can also reduce the effectiveness of the heat exchanger over time.Furthermore, particularly in exhaust gas recirculation coolers, which cool the exhaust gas that is recirculated to the inlet, acidic compounds may be present in the condensate, causing deterioration of the cooler and / or the downstream components.

[0003] DE 10 2009 037 923 A1 discloses an arrangement for recirculating and cooling exhaust gas from an internal combustion engine. DE 10 2010 034 131 A1 discloses a method for regulating the temperature of the gas system of an internal combustion engine. DE 10 2013 111 118 A1 discloses an engine control system and an engine method.

[0004] To prevent the accumulation of condensate in the heat exchanger, a heat exchanger bypass line can be provided. During conditions where condensate is expected to form in the radiator, the air normally provided to the heat exchanger can be routed through the bypass line to prevent potential condensate deposition within the heat exchanger. Such bypass lines can be expensive and increase the complexity of the engine control system strategy. Furthermore, it can be difficult to accurately predict when condensation may form, which can lead to unnecessary air redirection and increased temperature and reduced density of the charge air.

[0005] The inventors have recognized the problems of the above approach and provide a method that at least partially addresses them. In one embodiment, a method for an engine includes increasing exhaust gas recirculation (EGR) flow in response to condensation in an EGR cooler.

[0006] In this way, the flow of EGR may be increased in response to condensation in an EGR cooler. In one example, the EGR flow may be increased when an estimated amount of accumulated condensate in the EGR cooler exceeds a threshold. The amount of accumulated condensate in the EGR cooler may be estimated based on both an amount of condensate forming within the EGR cooler and an amount of condensate evaporating from the EGR cooler over a predetermined period of time. By tracking the amount of condensate formed as well as the amount of evaporated condensate, the amount of condensate actually accumulating in the heat exchanger may be more precisely determined. Furthermore, by adjusting the EGR flow in response to condensation in the cooler, the condensate may be removed without using a complex bypass piping system, or in addition to such a bypass piping system.

[0007] The above advantages and other advantages and features of the present description will become apparent from the following detailed description taken alone or in conjunction with the accompanying drawings.

[0008] It will be understood that the above summary is provided to provide, in simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify principal or essential features of the claimed subject matter, the scope of which is defined solely in the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that eliminate potential disadvantages mentioned above or in any part of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS They show: Fig. 1 is a schematic diagram of an embodiment of an engine with a turbocharger and an exhaust gas recirculation system. Fig. 2 is an abstracted flow diagram illustrating a method for detecting and removing condensate from the engine heat exchanger according to an embodiment of the present disclosure. Fig. 3 is a flowchart illustrating a method for estimating an amount of condensate formed within an EGR cooler according to an embodiment of the present disclosure. Fig. 4 is a flowchart illustrating a method for estimating an amount of vaporized condensate within an EGR cooler according to an embodiment of the present disclosure. Fig. 5 is a flowchart illustrating a method for removing condensate within an EGR cooler according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0009] Engine heat exchangers such as EGR coolers and intercoolers can accumulate condensate under certain conditions. The accumulated condensate can be carried into the engine, where, if present in large quantities, it can cause misfire and other combustion problems or component damage. To prevent the accumulation of condensate within an engine heat exchanger, the amount of condensate formed and evaporated in the heat exchanger can be tracked using a condensation model. The condensation model can output condensate formed and evaporated based on speed- and load-dependent operating parameters, such as EGR rate, boost pressure, and mass air flow. If condensate accumulates in the heat exchanger to a threshold level, an engine actuator can be adjusted to remove the condensate from the heat exchanger. Fig. 1 shows an engine having a plurality of heat exchangers and a controller adapted to carry out the methods of Fig. 2 to 5 are configured.

[0010] In relation to Fig. 1 illustrates a schematic diagram of a cylinder of a multi-cylinder engine 10, which may be incorporated into a propulsion system of an automobile. Engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 132 via an input device 130. In this example, input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Combustion chamber (e.g., cylinder) 30 of engine 10 may include combustion chamber walls 32 with piston 36 disposed therein. In some embodiments, the surface of piston 36 within combustion chamber 30 may include a bowl. Piston 36 may be coupled to crankshaft 40 such that reciprocal motion of the piston is translated into rotational motion of the crankshaft.The crankshaft 40 may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Furthermore, a starter motor may be coupled to the crankshaft 40 via a flywheel to enable starting operation of the engine 10.

[0011] Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and expel combustion gases via exhaust passage 48. Intake manifold 44 and exhaust passage 48 may be selectively connected to combustion chamber 30 via the respective intake valve 52 or exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.

[0012] The intake valve 52 may open and close according to the lobes of the intake cam 51. Similarly, the exhaust valve 54 may open and close according to the lobes of the exhaust cam 53. The phase of the intake cam 51 and exhaust cam 53 may be varied relative to the crankshaft 40. Alternatively, the variable valve actuator may be electro-hydraulic or any other mechanism for enabling valve actuation. During some conditions, the controller 12 may vary the signals provided by the actuators coupled to the intake cam 51 and exhaust cam 53 to control the opening and closing timing of the corresponding intake and exhaust valves. The position of the intake valve 52 and exhaust valve 54 may be determined by the valve position sensors 55 and 57, respectively.In alternative embodiments, one or more intake and exhaust valves may be actuated by one or more electric actuators and utilize one or more of cam profile control (CPS), variable camshaft timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) to vary valve operation. For example, cylinder 30 may alternatively have an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation with CPS and / or VCT. Fuel injector 66 is shown directly coupled to combustion chamber 30 for injecting fuel directly therein, proportional to the pulse width of signal FPW received from controller 12 via electronic driver 68. In this manner, fuel injector 66 provides what is known as direct injection of fuel into combustion chamber 30.The fuel injector may be located, for example, on the side of the combustion chamber or on top of the combustion chamber. Fuel may be delivered to the fuel injector 66 via a fuel system (not shown) that includes a fuel tank, a fuel pump, and a fuel rail.

[0013] The ignition system 88 may, in select operating modes, provide an ignition spark to the combustion chamber 30 using the spark plug 92 in response to an advance spark signal SA from the controller 12. Although the ignition components are illustrated, in some embodiments, the combustion chamber 30 or one or more other combustion chambers of the engine 10 may be operated in a compression ignition mode with or without an ignition spark.

[0014] The intake passage 42 may include throttle plates 62 and 63 with throttle discs 64 and 65, respectively. In this particular example, the positions of the throttle discs 64 and 65 may be varied by the controller 12 via signals provided to an electric motor or actuator included with the throttle plates 62 and 63, in a configuration commonly referred to as electronic throttle control (ETC). In this manner, the throttle plates 62 and 63 may be operated to vary the intake air provided to the combustion chamber 30 and other engine cylinders. The positions of the throttle discs 64 and 65 may be provided by the controller 12 via throttle position signals TP. Pressure, temperature, and mass air flow may be measured at various locations along the intake passage 42 and intake manifold 44.For example, intake passage 42 may include a mass air flow sensor 120 for measuring the clean air mass flow entering through throttle 63. The clean air mass flow may be communicated to controller 12 via the MAF signal.

[0015] The engine 10 may further include a compression device such as a turbocharger or a supercharger having at least one compressor 162 disposed upstream of the intake manifold 44. For a turbocharger, the compressor 162 may be driven at least partially by a turbine 164 (e.g., via a shaft) disposed along the exhaust passage 48. For a supercharger, the compressor 162 may be driven at least partially by the engine and / or an electric machine and may not include a turbine. Therefore, the amount of compression provided to one or more cylinders of the engine via a turbocharger or supercharger is varied by the controller 12. A charge air cooler 154 may be included downstream of the compressor 162 and upstream of the intake valve 52. The charge air cooler 154 may be configured to cool gases heated, for example, by compression by the compressor 162.In one embodiment, charge air cooler 154 may be located upstream of throttle valve 62. Pressure, temperature, and mass air flow may be measured downstream of compressor 162, such as with sensor 145 or 147. The measured results may be communicated to controller 12 from sensors 145 and 147 via signals 148 and 149, respectively. Pressure and temperature may be measured upstream of compressor 162, such as with sensor 153, and communicated to controller 12 via signal 155.

[0016] Further, in the disclosed embodiments, an EGR system may direct a desired portion of exhaust gas from the exhaust passage 48 to the intake manifold 44. Fig. 1 shows a high-pressure EGR system and a low-pressure EGR system, however, an alternative embodiment may have only a low-pressure EGR system. The high-pressure EGR is routed through the high-pressure EGR passage 140 from upstream of the turbine 164 to downstream of the compressor 162. The amount of high-pressure EGR provided to the intake manifold 44 may be varied by the controller 12 via the high-pressure EGR valve 142. The low-pressure EGR is routed through the low-pressure EGR passage 150 from downstream of the turbine 164 to upstream of the compressor 162. The amount of low-pressure EGR provided to the intake manifold 44 may be varied by the controller 12 via the low-pressure EGR valve 152. The high pressure EGR system may include a high pressure EGR cooler 146 and the low pressure EGR system may include the low pressure EGR cooler 158 to transfer heat from the EGR gases, for example, into the engine coolant.

[0017] Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture in the combustion chamber 30, for example, to control NOx production. Therefore, it may be desirable to measure or estimate the EGR mass flow rate. The EGR sensors may be located within the EGR passages and provide an indicator of one or more of mass flow rate, pressure, temperature, O2 concentration, and exhaust gas concentration. For example, a high-pressure EGR sensor 144 may be located within the high-pressure EGR passage 140.

[0018] In some embodiments, one or more sensors may be disposed within the low-pressure EGR passage 150 to provide an indication of one or more of the pressure, temperature, and air-fuel ratio of the exhaust gas recirculated through the low-pressure EGR passage 150. The exhaust gas redirected through the low-pressure EGR passage 150 may be diluted with fresh intake air at the mixing point located at the junction of the low-pressure EGR passage 150 and the intake passage 42. In particular, dilution of the EGR flow may be adjusted by adjusting the low-pressure EGR valve 152 in coordination with a first air intake throttle 63 (located in the air intake passage of the air intake, upstream of the compressor).

[0019] A fractional dilution of the low-pressure EGR flow may be derived from the output of a sensor 145 in the engine intake gas stream. Specifically, sensor 145 may be located downstream of the first intake throttle 63, downstream of the low-pressure EGR valve 152, and upstream of the second main intake throttle 62, so that the low-pressure EGR dilution at or near the main intake throttle can be precisely determined. Sensor 145 may, for example, be an oxygen sensor such as a UEGO sensor.

[0020] Exhaust sensor 126 is shown coupled to exhaust passage 48 downstream of turbine 164. Sensor 126 may be any suitable sensor for providing an indication of an exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wideband exhaust oxygen sensor), a two-stage oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. In one embodiment, exhaust sensor 126 may be a NOx sensor configured to provide an indication of engine output NOx levels, e.g., NOx levels in the exhaust downstream of the engine and upstream of any emissions control devices.

[0021] The emission control devices 71, 72, and 76 are shown arranged along the exhaust passage 48 downstream of the exhaust gas sensor 126. In the illustrated embodiment, the device 71 may be a selective catalyst reduction (SCR) system, while the devices 72 and 76 may be a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), three-way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. For example, the device 72 may be a DOC, and the device 76 may be a DPF. In some embodiments, the DPF 76 may be downstream of the SCR 71 and DOC 72 (as in Fig. 1), while in other embodiments, the DPF 76 may be arranged upstream of the DOC 72. Alternative arrangements are also possible in some embodiments, such as the DOC 72 and / or DPF 76 being arranged upstream of the SCR 71. If the device 71 is an SCR system, a reductant tank 73 may be provided for storing reductant such as urea or NH3. The tank 73 may be coupled to an injector 75 for injecting reductant into the exhaust gas upstream of the device 71 or into the device 71 to reduce NOx in the device 71. Furthermore, a mixer 74 may be provided to ensure adequate mixing of the reductant with the exhaust stream. Urea may be injected in proportion to an amount of NOx in the engine-derived exhaust entering the SCR.An additional NOx sensor 127 may be present downstream of device 71, 72 and 76 to provide an indication of device efficiency by comparing the NOx reading downstream of sensor 127 with the NOx reading of sensor 126.

[0022] The control 12 is in Fig. 1 as a microcomputer including the microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown in this example as a read-only memory chip 106, random access memory 108, keep-alive memory 110, and a data bus. The controller 12, in addition to the signals previously described, may receive various signals from sensors coupled to the engine 10, including the induced mass air flow (MAF) measurement from the mass air flow sensor 120; the engine coolant temperature (ECT) from the temperature sensor 112 coupled to the cooling sleeve 114; the profile ignition pickup (PIP) signal from the Hall effect sensor 118 (or other type) coupled to the crankshaft 40; and the throttle position (TP) from a throttle position sensor, and the absolute manifold pressure signal MAP from sensor 122.The engine speed signal, RPM, may be generated by controller 12 from the PIP signal. The manifold pressure signal, MAP, from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, and vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Further, this sensor, along with the sensed engine speed, may provide an estimate of the charge (including air) being introduced into the cylinder. In one example, sensor 118, which is also used as an engine torque sensor, may generate a predetermined number of equally spaced pulses for each revolution of the crankshaft.

[0023] The read-only storage medium 106 may be programmed with computer-readable data executable by the processor 102 to perform the methods described below, as well as other variations anticipated but not specifically listed.

[0024] As described above, Fig. 1 only one cylinder of a multi-cylinder engine, and each cylinder may similarly have its own set of intake and exhaust valves, fuel injector, spark plug, etc.

[0025] With reference to Fig. 2 illustrates an abstracted method 200 for controlling condensate accumulation in an engine heat exchanger. Method 200 may be executed by an engine controller, such as controller 12, according to instructions stored therein. The heat exchanger may be an EGR cooler (such as cooler 146 or 158), a charge air cooler (such as cooler 154), or another heat exchanger.

[0026] Method 200 includes determining ambient and engine operating parameters at 202. The ambient operating parameters may include humidity, temperature, and pressure of the air entering the engine's intake system. The engine operating parameters may include engine speed and load, EGR rate, mass air flow, boost pressure, intake air temperature at the inlet of the heat exchanger, air-fuel ratio, and other parameters.

[0027] At 204, the amount of condensate formed within the heat exchanger is estimated. The amount of condensate formed can be determined by using a condensation model that estimates condensate formation as a function of the moisture content of air entering the heat exchanger and heat exchanger conditions such as pressure, temperature, and mass flow rate of air through the heat exchanger. Additional details regarding the estimation of the amount of condensate formed are described below with reference to Fig. 3 provided.

[0028] At 206, the amount of condensate evaporated within the heat exchanger is estimated. Just as with the amount of condensate formed, the amount of evaporated condensate can be determined by using the condensation model. The amount of evaporated condensate can depend on the air mass flow through the heat exchanger, the temperature at the outlet of the heat exchanger, and the pressure of the heat exchanger. Furthermore, the amount of evaporated condensate can also include the condensate in the heat exchanger that is entrained by the air flowing through the exchanger. Additional details regarding the estimation of the amount of evaporated condensate are described below with reference to Fig. 4 provided.

[0029] At 208, the amount of condensate formed and evaporated condensate with the heat exchanger is monitored to determine an estimated amount of accumulated condensate. At 210, it is determined whether the amount of accumulated condensate is above a threshold. The threshold may be any suitable threshold. In one example, the threshold may be zero, so any amount of accumulated condensate may be above the threshold. In other examples, the threshold may be greater than zero, so a small amount of accumulated condensate is tolerated, but the threshold may be less than the amount of condensate that could cause misfire or other engine problems if directed into the engine. If the accumulated condensate is not above the threshold, method 200 returns to 208 to continue monitoring condensate formation and evaporation.

[0030] If the accumulated condensate is above the threshold, method 200 proceeds to 212 to adjust one or more operating parameters to remove the condensate and / or to prevent future accumulation of condensate within the heat exchanger. For example, if the heat exchanger is an EGR cooler, the EGR valve that controls the amount of exhaust gas recirculated to the intake may be opened to increase the amount of EGR flowing through the cooler. In another example, if the heat exchanger is a charge air cooler, the EGR valve, throttle valve, turbocharger wastegate, and / or compressor bypass valve may be adjusted to vary the speed, mass air flow rate, temperature, etc. of the intake air through the charge air cooler.In another example, the amount of coolant flowing to the EGR cooler or the charge air cooler may be adjusted to increase the temperature of the EGR cooler or charge air cooler. For example, a coolant bypass or flow metering valve may be present in the coolant flow line leading to the EGR cooler and / or charge air cooler, and this valve may be closed to reduce coolant flow to the corresponding cooler. Adjusting the operating parameters in response to accumulated condensate above the threshold is discussed below with reference to FIG. Fig. 5 described in more detail.

[0031] Fig. 3 to 5 are flowcharts illustrating various methods for controlling condensate accumulation in an EGR cooler. Although the methods of Fig. 3 to 5 can be applied to other heat exchangers (e.g., charge air coolers), some details of the procedures are specific to the type of heat exchanger to which the procedure refers; therefore, the procedures below are explained with reference to an EGR cooler. Additional details regarding the application of the procedures below to a charge air cooler are also presented. With reference to Fig. 3 illustrates a method 300 for estimating the amount of condensate formed within an EGR cooler using a condensation model. The method 300 may be executed by the controller 12 to determine an amount of condensate formed within the EGR cooler at a given time. As described above with reference to Fig. 2, the amount of condensate formed can be monitored at any calculated time over a predetermined period to determine how much condensate has accumulated in the EGR cooler.

[0032] Method 300 includes determining engine speed and load and other parameters at 302. The amount of condensate formed in the EGR cooler is speed and load dependent because several factors that affect condensation, such as EGR rate, are scheduled based on speed and load. Additional parameters that may be determined include ambient humidity, mass air flow, boost pressure, EGR cooler inlet temperature, etc. At 304, the moisture content of the intake air entering the engine is determined based on the humidity, mass air flow, pressure, and temperature of the intake air. In one example, the moisture content of the intake air may be determined based on the following equation: MCin=Specific Humidity×MAF

[0033] The specific humidity can be calculated using the following equation: Specific humidity = 0.622 (Pv / (P−Pv)) where P is the inlet air vapor partial pressure, which can be determined from a graph of water saturation evaluation pressure versus inlet air temperature.

[0034] At 306, the moisture content of the EGR downstream of the EGR cooler is estimated based on the EGR cooler outlet temperature, EGR cooler pressure, and mass air flow. In one example, the moisture content of the EGR downstream of the cooler may be determined using the following equation: MCEGR=MAF×0.622×P+3.07×102(Toutlet)+6.47 / (Cooler Pressure−P) where, similar to above, P is the partial water vapor pressure, which is determined as a function of the EGR cooler outlet temperature. The EGR cooler pressure can be equal to the boost pressure (if the EGR valve is located upstream on the hot side of the cooler) or it can be equal to 1.2 x boost pressure (if the EGR valve is located downstream on the cold side of the cooler). The EGR cooler outlet temperature can be determined based on the following equation: Tout=Tin−e×(Tin−Tcoolant) where T in is the temperature of the radiator inlet (measured by a sensor), e is the radiator effectiveness as a function of the air mass flow, as specified by the radiator manufacturer, and T coolant is the temperature of the coolant in the radiator.

[0035] At 308, the moisture content of the exhaust gas is estimated based on the sum of the intake air moisture content, the EGR moisture content, and the moisture generated during combustion. The moisture generated during combustion is determined using the following equation: MCcombustion=fuel flow×(kgH2O / kgfuel)

[0036] The fuel flow can be determined by dividing the air mass flow by the air-fuel ratio, and kg(H2O) / kg(fuel) depends on the air-fuel ratio and the fuel composition. For example, at an air-fuel ratio of 14.5, 1 kg of diesel fuel produces 1.174 kg H2O. In other embodiments, the moisture content of the exhaust gas can be estimated based on the exhaust air-fuel ratio. In still other embodiments, an exhaust gas sensor (such as sensor 126 of Fig. 1) can be used to determine the humidity and thus the moisture content of the exhaust gas.

[0037] At 310, the amount of condensate formed in the cooler is estimated based on the exhaust moisture content and EGR rate determined above. Since only a portion of the exhaust gas is routed to the EGR cooler, multiplying the exhaust moisture content by the EGR rate provides an estimate of the moisture content of the EGR entering the cooler. Furthermore, in some embodiments, the amount of condensate formed within the cooler may also be determined based on cooler conditions, such as cooler temperature, mass air flow through the cooler, cooler pressure, etc.

[0038] Therefore, procedure 300 issues Fig. 3 provides a method for estimating the amount of condensate formed within an EGR cooler. The amount of condensate formed can be determined using various speed- and load-dependent inputs, including EGR rate, air mass flow, gas temperature at the inlet of the EGR cooler, boost pressure, and air-fuel ratio, as well as speed- and load-independent inputs, including cooler specifications (e.g., effectiveness), temperature of the coolant in the cooler, and humidity. The condensation model used to estimate the amount of condensate formed is based in part on the amount of EGR flowing through the cooler. However, it can be assumed that even when EGR is deactivated (e.g., when the EGR valve is fully closed), a small amount of EGR passes through the EGR valve.There is also a small amount of leakage associated with bypassing, or EGR can leak through the bypass into the cooler and condense over time. Therefore, even if the EGR rate is set to zero, the condensation model can use a preset small amount of EGR to estimate the amount of condensate formed.

[0039] As previously explained, method 300 is described herein as determining the amount of condensate formed in an EGR cooler. However, the method may be used to determine the amount of condensate formed in another heat exchanger, such as a charge air cooler. The amount of condensate formed in the charge air cooler is not affected by the moisture content of the exhaust gas or EGR, except when a low-pressure EGR system is present that introduces low-pressure EGR upstream of the turbocharger compressor inlet, and therefore, the condensate in the charge air cooler may depend on the moisture content of the air entering the charge air cooler (e.g., humidity), air mass flow, charge air cooler temperature, and charge air cooler pressure. The charge air cooler temperature may include the temperature of the coolant flowing through the charge air cooler as well as the temperature at the charge air cooler inlet.However, if low pressure EGR is introduced into the intake air upstream of the compressor, the amount of low pressure EGR can also be used to determine the amount of condensate formed in the intercooler.

[0040] With reference to Fig. 4 illustrates a method 400 for estimating the amount of evaporated condensate in the EGR cooler based on the condensation model described above. Condensate may form in the cooler during certain conditions (e.g., low air mass flow, relatively cool exhaust gas entering the cooler). However, under other conditions, condensate previously formed in the cooler may evaporate and / or be entrained by the exhaust gas flowing through the cooler. Thus, to obtain an accurate overall determination of the total amount of accumulated condensate within the EGR cooler, both the amount of formed and evaporated condensate are estimated. Method 400 may be executed by controller 12 according to instructions stored therein.

[0041] Method 400 includes, at 402, determining the maximum theoretical EGR saturated moisture content based on the EGR cooler temperature, pressure, and EGR specific humidity. The maximum theoretical EGR saturated moisture content is determined using the same equation used with respect to Fig. 3 to calculate the moisture content in the EGR after leaving the cooler: MCEGR=MAF×0.622×P+3.07×102(Toutlet)+6.47 / (Cooler Pressure−P)

[0042] Therefore, the moisture content in the EGR after passing through the cooler provides an approximation of the amount of moisture that was not captured in the cooler and the amount of condensate that evaporated from the cooler. At 404, it is determined whether the maximum theoretical EGR saturation moisture content is less than the current EGR flow rate. If the maximum EGR saturation moisture content is not less than the current EGR flow rate, the EGR gas flow can be assumed to be entirely steam, and method 400 proceeds to 406 to set the amount of evaporated condensate in the cooler equal to the EGR flow rate.

[0043] If the maximum theoretical EGR saturation moisture content is greater than the EGR flow rate, method 400 proceeds to 408 to set the amount of vaporized condensate equal to the maximum theoretical EGR saturation moisture content. Method 400 then ends.

[0044] Therefore, method 400 provides for determining the amount of vaporized condensate in an EGR cooler. As previously described, the amount of vaporized condensate may also include the amount of condensate entrained by the exhaust gas flowing through the cooler. The amount of entrained condensate may be based on the flow velocity of the exhaust gas through the cooler. Furthermore, a similar method may be applied to determining the amount of vaporized condensate in a charge air cooler. The vaporized condensate in a charge air cooler may be determined similarly to the EGR cooler using mass air flow, temperature at the outlet of the charge air cooler, pressure in the charge air cooler, and saturation pressure of the intake air at a given cooler outlet temperature.

[0045] Fig. 5 is a flowchart illustrating a method 500 for removing accumulated condensate from an EGR cooler. Method 500 may be executed by a controller 12 according to instructions stored therein in response to an indication that the amount of accumulated condensate, determined based on methods 300 and 400 as presented above, is above a threshold. Method 500 removes accumulated condensate by increasing the amount of EGR flowing through the cooler. However, in some embodiments, to avoid interrupting the EGR control strategy, EGR may be increased for condensation control only during selected conditions described below.

[0046] The method 500 includes determining at 502 whether the accumulated condensate in the EGR cooler is below the threshold, similar to the method described above with respect to Fig. 2. If the accumulated condensate is below the threshold, method 500 proceeds to 504 to cause EGR to flow according to a first flow. The first flow may be the standard EGR flow flow, which sets the EGR rate based on engine speed and load to maintain intake oxygen at a certain level to control emissions. Method 500 then returns.

[0047] If the accumulated condensate is not below the threshold, method 500 proceeds to 506 to flow EGR according to a second, different schedule to remove the condensate and / or to prevent further accumulation of condensate in the cooler. Flowing EGR according to the second schedule may include flowing EGR at a rate selected from a desired table, as indicated at 508. The desired table may be any EGR rate table already stored in the controller's memory or may be an EGR rate table specifically assigned for condensate removal. The selected EGR rate may be determined at 510 based on a condensate model (e.g., the model described above with respect to Fig. 3 and Fig. 4) be changed to allow EGR to flow under conditions where condensate is not formed. The selected EGR rate may be further changed at 512 to maintain combustion stability. Since EGR may be activated for condensate removal during conditions where EGR is not normally activated, the selected EGR rate may be changed to ensure that combustion instability does not occur, to ensure that control strategies based on the amount of EGR are not interrupted, and to ensure that EGR does not cause additional condensate accumulation instead of its removal. In this way, for a given engine speed and load point, the amount of EGR directed to the intake when the accumulated condensate is below the threshold may be different from the amount directed to the intake when the accumulated condensate is above the threshold.

[0048] In some embodiments, EGR may flow according to a second schedule only if permitted by the constraints already imposed on the EGR system. For example, if EGR is currently enabled, it may remain in the first schedule rather than switching to the second schedule. Further, if EGR is disabled to prevent degradation, it may remain disabled. Therefore, indicated as optional at 514, EGR may flow according to the second schedule only if EGR is currently disabled due to emissions control. EGR is typically enabled to maintain a lower intake oxygen concentration, which in turn lowers combustion temperatures to reduce emissions such as NOx.Under certain conditions, such as when operating the engine after a cold start, or during conditions of relatively high engine load and / or speed, EGR may be disabled because NOx control is not indicated, or because flowing EGR under these conditions may cause misfire or other unstable combustion conditions. If EGR is currently enabled, adjusting the amount of EGR to remove condensate may interfere with standard NOx control strategies, and EGR may be set according to the conventional initial flow. Additionally, EGR may currently be disabled to prevent an overtemperature event or other degradation.If EGR is currently disabled due to or to prevent degradation of the engine or other components, EGR cannot be enabled for condensate control because doing so may cause degradation of the engine or other components. After enabling EGR to remove condensate, method 500 returns.

[0049] Although method 500 adjusts an EGR valve in response to accumulated condensate in an EGR cooler when the accumulated condensate in an intercooler exceeds a threshold, other engine actuators may be adjusted to remove the condensate from the intercooler. For example, a turbocharger wastegate may be adjusted to increase or decrease boost pressure. In another example, the throttle valve may be adjusted to increase the velocity of intake air flowing through the intercooler.

[0050] Therefore, the methods described above provide for the detection and removal of condensate in an engine heat exchanger, particularly an EGR cooler or an intercooler. The above methods depend on a condensation model that predicts both the condensate formed and the evaporated condensate. The method described above with reference to Fig. 3 and Fig. The model described in Section 4 uses the free flow temperature of the gas flowing through the heat exchanger and does not consider the effect of the temperature of the heat exchanger walls or interface. However, the model can be modified to account for these effects. Furthermore, the model output can be further adjusted based on the EGR cooler coolant temperature, gas temperature, and other factors.

[0051] In one embodiment, the method for an engine includes adjusting an engine actuator based on an estimated accumulated condensate in an engine heat exchanger, wherein the estimated accumulated condensate is determined from an amount of formed condensate and an amount of evaporated condensate within the engine heat exchanger over a predetermined period of time.

[0052] In a first example, the actuator may include a wastegate, and the heat exchanger may include an intercooler. The amount of condensate formed and evaporated within the intercooler may be estimated based on the moisture content of the intake air entering the intercooler, a temperature of the intercooler, a boost pressure, and air mass flow through the intercooler. The moisture content of the intake air may be based on the humidity, air mass flow, temperature, and pressure of the intake air upstream of the intercooler.

[0053] In a second example, the actuator may include an exhaust gas recirculation (EGR) valve, and the heat exchanger may include an EGR cooler. The amount of condensate formed within the EGR cooler may be estimated based on the moisture content of the exhaust gas directed to the atmosphere and the amount of EGR directed into the engine. The moisture content of the exhaust gas may depend on the moisture generated during combustion, the moisture content of the intake air directed into the engine, and the moisture content of the EGR directed into the engine; the moisture content of the intake air may depend on the relative intake air humidity, air mass flow, pressure, and temperature; and the moisture content of EGR directed into the engine may depend on the air mass flow, EGR cooler outlet temperature, and EGR cooler pressure.The amount of evaporated condensate within the EGR cooler can be estimated based on the air mass flow, the EGR cooler outlet temperature, and the EGR cooler pressure. The EGR valve can be adjusted based on the accumulated condensate in the EGR cooler, opening the EGR valve to increase the EGR directed to the intake.

[0054] In another embodiment, the method for an engine includes adjusting an exhaust gas recirculation (EGR) valve based on an estimated accumulated condensate in an EGR cooler, wherein the estimated accumulated condensate includes an amount of formed condensate and an amount of vaporized condensate within the EGR cooler over a predetermined period of time. The EGR valve may be opened to increase the EGR directed into the intake.

[0055] The amount of condensate formed in the EGR cooler may be determined based on the moisture content of the intake air entering the engine, the moisture content of the exhaust gas exiting the engine, the moisture content of the EGR directed to the intake, and the amount of EGR directed to the intake. The amount of condensate formed in the EGR cooler may be further determined based on the EGR cooler temperature, EGR cooler effectiveness, and EGR temperature. The amount of vaporized condensate within the EGR cooler may be determined based on the mass air flow, the EGR cooler outlet temperature, and the EGR cooler pressure.

[0056] In another embodiment, a method for an engine includes estimating accumulated condensate in an EGR cooler based on formed and evaporated condensate within an EGR cooler, and, if the accumulated condensate is above a threshold, adjusting an EGR valve during selected conditions to increase EGR passed through the EGR cooler to remove the accumulated condensate. The selected conditions may include the EGR valve being fully closed before adjusting the EGR valve. Adjusting the EGR valve to increase EGR passed through the EGR cooler may further include adjusting the EGR valve to supply an amount of EGR selected based on engine operating conditions and an amount of condensate expected to accumulate in the EGR cooler.The amount of accumulated condensate in the EGR cooler may be further estimated based on the coolant temperature of the EGR cooler.

[0057] It will be appreciated that the configurations and methods disclosed herein are exemplary, and that these specific embodiments are not to be considered limiting, as numerous variations thereof are possible. For example, the technology described above may be applied to V-6, I-4, I-6, V-12, horizontally opposed four, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0058] The following claims highlight certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or an equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements and neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims that are broader, narrower, the same, or different in scope with respect to the original claims are intended to be included within the subject matter of the present disclosure.

Claims

[1] A method for an engine (10) comprising: Increasing exhaust gas recirculation (EGR) flow in response to condensation in an EGR cooler (146, 158), characterized by in that the condensation is an estimated amount of accumulated condensate, the estimated amount of accumulated condensate being based on an amount of condensate formed within the EGR cooler (146, 158) over a predetermined period of time and an amount of condensate evaporated within the EGR cooler (146, 158) over the predetermined period of time. [2] The method of claim 1, further comprising, when the estimated amount of accumulated condensate is below a threshold, flowing EGR according to a first schedule, and, when the estimated amount of accumulated condensate is above the threshold, flowing EGR according to a different second schedule. [3] The method of claim 1, wherein the amount of condensate formed in the EGR cooler (146, 158) is determined based on the moisture content of the intake air entering the engine (10), the moisture content of the exhaust gas exiting the engine (10), the moisture of the EGR directed to the inlet and an amount of EGR directed to the inlet, the EGR cooler temperature, EGR cooler effectiveness and EGR temperature. [4] The method of claim 1, wherein the amount of vaporized condensate in the EGR cooler (146, 158) is determined based on a mass air flow, the EGR cooler outlet temperature, and the EGR cooler pressure. [5] A method for an engine (10) comprising: Adjusting an engine actuator based on an estimated accumulated condensate in an engine heat exchanger, wherein the estimated accumulated condensate is determined from an amount of condensate formed within the engine heat exchanger over a predetermined period of time and an amount of condensate evaporated within the engine heat exchanger over the predetermined period of time, characterized by that the actuator comprises an exhaust gas recirculation valve (EGR valve) and wherein the heat exchanger comprises an EGR cooler (146, 158). [6] The method of claim 5, wherein the actuator comprises a wastegate and wherein the heat exchanger comprises a charge air cooler (154). [7] The method of claim 6, further comprising estimating the amount of condensate formed and evaporated within the charge air cooler (154) based on the moisture content of the intake air entering the charge air cooler (154), a temperature of the charge air cooler (154), a boost pressure, and a mass air flow through the charge air cooler (154). [8] The method of claim 7, wherein the moisture content of the intake air is based on the humidity, the air mass flow, the temperature and the pressure of the intake air upstream of the charge air cooler (154). [9] The method of claim 5, further comprising estimating the amount of condensate formed within the EGR cooler (146, 158) based on the moisture content of the exhaust gas directed to the atmosphere and the amount of EGR directed into the engine (10). [10] A method according to claim 9, wherein the moisture content of the exhaust gas depends on the moisture generated during combustion, the moisture content of the intake air passed into the engine (10) and the moisture content of EGR passed to the engine (10). [11] The method of claim 10, wherein the moisture content of the inlet air is dependent on the relative inlet air humidity, the air mass flow, the pressure and the temperature. [12] The method of claim 9, wherein the moisture content of the EGR directed to the engine (10) is dependent on the air mass flow, the EGR cooler outlet temperature, and the EGR cooler pressure. [13] The method of claim 9, further comprising estimating the amount of vaporized condensate within the EGR cooler (146, 158) based on the mass air flow, the EGR cooler outlet temperature, and the EGR cooler pressure. [14] The method of claim 5, wherein adjusting the EGR valve based on the accumulated condensate in the EGR cooler (146, 158) further comprises opening the EGR valve to increase EGR directed through the inlet. [15] Method for an engine (10), comprising: Estimating an amount of accumulated condensate in an EGR cooler (146, 158) based on formed and evaporated condensate within the EGR cooler (146, 158); and when the accumulated condensate is above a threshold, adjusting an EGR valve during selected conditions to increase the EGR passed through the EGR cooler (146, 158) to remove accumulated condensate. [16] The method of claim 15, wherein the selected conditions include the EGR valve in a fully closed position prior to adjusting the EGR valve. [17] The method of claim 15, wherein adjusting the EGR valve to increase EGR passed through the EGR cooler (146, 158) further comprises adjusting the EGR valve to deliver an amount of EGR selected based on engine operating conditions and further based on an amount of condensate expected to accumulate in the EGR cooler (146, 158). [18] The method of claim 15, wherein the amount of accumulated condensate in the EGR cooler (146, 158) is further estimated based on the coolant temperature of the EGR cooler (146, 158).

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