Method for flushing condensate from an intercooler

Abstract

Method for an engine (10), comprising: in response to a condensate level in a charge air cooler (166), increasing engine airflow more than requested by a vehicle operator (132) without increasing engine torque by adjusting an engine actuator to maintain torque.

Description

Background / Brief description

[0001] Turbocharged and supercharged engines may be configured to compress ambient air entering the engine to increase power. Air compression can cause an increase in air temperature; therefore, an intercooler may be used to cool the heated air, increasing its density and further enhancing the engine's potential power. Ambient air from outside the vehicle flows over the charge air cooler (CAC) to cool the intake air flowing through the interior of the CAC. Condensation can form in the CAC when the ambient air temperature decreases or during humid or rainy conditions where the intake air is cooled below the water dew point. Condensation can accumulate at the bottom of the CAC or in the internal passages and cooling turbulators.When torque is increased, such as during acceleration, the increased mass air flow can pull condensate from the CAC, draw it into the engine, and increase the likelihood of engine stall.

[0002] US 2010 / 0 332 075 A1 relates to a condensation monitoring system for a vehicle, which includes a humidity estimation module and a condensation detection module. DE 10 2010 007 092 A1 describes an exhaust gas recirculation system for an internal combustion engine, wherein the condensate formed in the charge air cooler is automatically extracted by the negative pressure in the fresh air tract and fed to the combustion process. DE 10 2013 111 118 A1 discloses methods and systems for flushing condensate from a charge air cooler to an engine intake.

[0003] Other attempts to address engine misfires due to condensate ingestion involve preventing condensate formation. However, the inventors have identified potential problems with such methods. In particular, even if some methods can reduce or slow condensate formation in the CAC, condensate can still build up over time. If this formation cannot be stopped, condensate ingestion during acceleration can lead to engine misfires.

[0004] According to the invention, methods having the features of claims 1 and 7 and an engine system having the features of claim 18 are provided.

[0005] Another method to prevent engine misfires due to condensate ingestion involves trapping and / or draining the condensate from the CAC. While this may reduce condensate levels in the CAC, it transports the condensate to another location or reservoir, which may be subject to other condensate problems such as freezing and corrosion.

[0006] In one example, the problems described above can be addressed by a method for periodically purging condensate from the CAC during safe vehicle operating conditions. A CAC purge cycle can be initiated in response to a condensate level when the operating requirements for stable combustion are met. By increasing airflow through the CAC, controlled amounts of condensate can be purged into the engine without causing misfires. The increase in engine airflow can be counteracted by adjusting various engine actuators to maintain the torque demand. In this way, the vehicle operator may not be alerted to the purge cycle. By performing this purge routine, condensate levels in the CAC can be maintained at a low level to prevent engine misfires during normal vehicle operation.

[0007] It should be understood that the above summary is intended to introduce, in a simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any of the disadvantages noted above or elsewhere in this disclosure. Short description of the drawings Fig. 1 is a schematic diagram of an example engine system that includes a charge air cooler. Fig. Figure 2 shows a detailed flow diagram of a process for purging condensate from a charge air cooler (CAC) based on operating conditions and condensate height. Fig. 3 shows a flowchart illustrating a method for determining the amount of condensate in a CAC according to an embodiment of the present disclosure. Fig. 4 shows a flowchart of a method for determining whether conditions exist to activate a proactive CAC purge routine. Fig. Figure 5 shows a flowchart of a method for performing a proactive CAC purge routine. Fig. 6 shows a flowchart of a method for setting a boundary knock limit and ignition timing based on humidity and condensate height in a CAC. Fig. 7 - 8 show exemplary condensate flushing processes. Fig. Figure 9 shows a graphical example of setting a boundary knock limit and spark timing in response to intake manifold humidity and CAC condensate height. Fig. Figure 10 shows a graphical example of adjusting ignition timing in response to purging condensate from an intercooler during a proactive purge cycle. Fig. Figure 11 shows a graphical example of adjusting ignition timing in response to purging condensate from a CAC during tip-in. Detailed description

[0008] The following description relates to systems and methods for purging condensate from a charge air cooler (CAC) of an engine system, such as the system of Fig. 1, while in response to condensate flow, engine actuators are also adjusted, including ignition timing. CAC condensate purging can occur in response to a driver-induced input, such as a tip-in condition. Alternatively, proactive condensate purging of the CAC can be performed in response to condensate height and other system variables. In both purging situations, engine actuators can be adjusted to maintain torque and improve engine performance. An engine controller can be configured to execute a control routine, such as the routine of Fig. 2, to estimate a condensate level in the CAC and react to a tip-in condensate drain or to perform a proactive condensate drain while adjusting the ignition timing accordingly. The controller can adjust the condensate level in the CAC based on a Fig. 3 presented model. A proactive emptying routine ( Fig. 5), where airflow through the CAC is proactively increased to flush condensate, can be performed when conditions exist to activate a proactive CAC drain routine ( Fig. 4). Alternatively, purging can occur due to the increased airflow during a tip-in. Engine torque can be maintained during purging by adjusting a number of engine controls. Example settings and purging procedures are shown in the Fig. 7 - 8. These examples illustrate the controls that may be required to initiate and execute a CAC purge cycle. Furthermore, the ignition timing can be adjusted by the controller based on changes in intake manifold humidity, which are determined in part by the condensate height in the CAC, as shown in Fig. 6. Example settings of the boundary knock limit and ignition timing based on humidity and CAC condensate quantity are shown in Fig. 9. Examples of purging processes with simultaneous adjustment of the ignition timing are shown in the Fig. 11 - 12 shown.

[0009] Now on Fig. 1, an internal combustion engine 10 comprising several cylinders is controlled by the electronic engine control 12, of which one cylinder in Fig. 1. The engine 10 includes a combustion chamber (cylinder) 30 and cylinder walls 32 with a piston 36 positioned therein, which is connected to a crankshaft 40. The combustion chamber 30 is shown communicating with an intake manifold 46 and an exhaust manifold 48 via an intake valve 52 and an exhaust valve 54, respectively. Each intake and exhaust valve can be actuated by an intake cam 51 and an exhaust cam 53. The opening and closing timing of the exhaust valve 54 can be adjusted with respect to crankshaft position via the cam phaser 58. The opening and closing timing of the intake valve 52 can be adjusted with respect to crankshaft position via the cam phaser 59. The position of the intake cam 51 can be determined by the intake cam sensor 55. The position of the exhaust cam 53 can be determined by the exhaust cam sensor 57.In this way, the controller 12 can control the cam timing through the phasers 58 and 59. Variable cam timing (VCT) can be advanced or retarded depending on various factors, such as engine load and engine speed (RPM).

[0010] In the illustration, the fuel injector 66 is positioned to inject fuel directly into the combustion chamber 30, known to those skilled in the art as direct injection. Alternatively, fuel may be injected into an intake port, known to those skilled in the art as port injection. The fuel injector 66 delivers liquid fuel proportional to the pulse width of the FPW signal from the controller 12. Fuel is delivered to the fuel injector 66 from a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail (not shown). The fuel injector 66 is supplied with operating power by driver 68, which is addressed by the controller 12. In one example, a two-stage high-pressure fuel system is used to produce higher fuel pressures.Additionally, the intake manifold 46 is shown communicating with an optional electronic throttle 62 that controls a position of the throttle plate 64 to control airflow from the intake charge chamber 44. The compressor 162 draws air from the air intake 42 to supply the intake charge chamber 44. Exhaust gases rotate the turbine 164, which is coupled to the compressor 162, which compresses air in the charge chamber 44. Various arrangements for driving the compressor may be provided. In a supercharger, the compressor 162 may be at least partially driven by the engine and / or an electric machine and may not include a turbine. Thus, the amount of compression provided to one or more cylinders of the engine via a turbocharger or supercharger may be varied by the controller 12.A turbocharger exhaust port 171 is a valve that allows exhaust gases to bypass the turbine 164 via a bypass passage 173 when the turbocharger exhaust port 171 is in an open state. Essentially, all exhaust gases flow through the turbine 164 when the exhaust port 171 is in a fully closed position.

[0011] Furthermore, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may direct a desired portion of the exhaust gases from the exhaust manifold 48 to the intake charge chamber 44 via the EGR passage 140. The amount of EGR supplied to the intake charge chamber 44 may be varied by the controller 12 via the EGR valve 172. Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture in the combustion chamber. Fig. 1 shows a high-pressure EGR system in which EGR is routed from upstream of a turbine of a turbocharger to downstream of a compressor of a turbocharger. In other embodiments, the engine may additionally or alternatively include a low-pressure EGR system in which EGR is routed from downstream of a turbine of a turbocharger to upstream of a compressor of the turbocharger. When operational, the EGR system may induce the formation of condensate from the compressed air, particularly when the compressed air is cooled by the charge air cooler, as described in more detail below. In particular, the EGR contains a large amount of water as a combustion byproduct. Because EGR is at a relatively high temperature and contains a lot of water, the dew point temperature may also be relatively high.Consequently, condensate formation from EGR can be even much higher than condensate formation from compressing air and lowering it to the dew point temperature.

[0012] The intake charge chamber 44 may further include the charge air cooler (CAC) 166 (e.g., an intercooler) to reduce the temperature of the turbocharged or boosted intake gases. In some embodiments, the CAC 166 may be an air-to-air heat exchanger. In other embodiments, the CAC 166 may be an air-to-liquid heat exchanger. The CAC 166 may include a valve for selectively modulating the flow rate of intake air passing through the charge air cooler 166 in response to condensation formation in the charge air cooler.

[0013] Hot charge air from compressor 162 enters the inlet of CAC 166, cools as it passes through CAC 166, and then exits to flow through throttle body 62 and into engine intake manifold 46. Ambient airflow from outside the vehicle may enter engine 10 through a vehicle front end and pass over the CAC to assist in cooling the charge air. Condensate may form and accumulate in the CAC when the ambient air temperature decreases or during humid or rainy weather conditions where the charge air is cooled below the water dew point. If the charge air contains recirculated exhaust gases, the condensate may become acidic and corrode the CAC housing. The corrosion can lead to leaks between the charge air, the atmosphere, and possibly the coolant in the case of water-to-air coolers.To reduce the accumulation of condensate and the risk of corrosion, condensate can be collected at the bottom of the CAC and then flushed into the engine under selected engine operating conditions, such as acceleration events. However, if the condensate is introduced into the engine all at once during an acceleration event, it may increase the possibility of engine misfire or combustion instability (in the form of late / slow burns) due to water ingestion. As described herein with reference to the . Fig. As outlined in Figures 2-5, condensate may be purged from the CAC to the engine under controlled conditions. This controlled purging may help reduce the likelihood of engine misfire events. In one example, condensate may be purged from the CAC using increased airflow under a tip-in condition. In another example, condensate may be proactively purged from the CAC by increasing airflow to the engine intake while controlling engine actuators to maintain the torque demand.

[0014] A distributorless ignition system 88 provides an ignition spark to the combustion chamber 30 via the spark plug 92 in response to the controller 12. A universal exhaust gas oxygen (UEGO) sensor 126 is shown connected to the exhaust manifold 48 upstream of a turbine 164. Alternatively, a dual-state oxygen sensor may be used in place of the UEGO sensor 126.

[0015] In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, a series configuration, or variations or combinations thereof. Furthermore, in some examples, other engine configurations, such as a diesel engine, may be employed.

[0016] During operation, each cylinder in engine 10 typically experiences a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, exhaust valve 54 generally closes and intake valve 52 opens. Air is introduced into combustion chamber 30 via intake manifold 46, and piston 36 moves to the bottom of the cylinder to increase the volume in combustion chamber 30. The position where piston 36 is near the bottom of the cylinder and at the end of its stroke (for example, when combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air in combustion chamber 30.The point at which piston 36 is at the end of its stroke and closest to the cylinder head (for example, when cylinder 30 is at its smallest volume) is generally referred to by those skilled in the art as top dead center (tdc). In an event referred to as injection, fuel is introduced into the combustion chamber. In an event referred to as ignition, the injected fuel is ignited by a known ignition means, such as spark plug 92, resulting in combustion. Ignition timing can be controlled to occur before the manufacturer's specified time (ignition advance) or after it (ignition retard). For example, ignition timing can be retarded by the MBT (maximum brake torque) control to control engine knock or advanced under high humidity conditions.In particular, the MBT may be advanced to accommodate the slow combustion rate. During the power stroke, the expanding gases push the piston 36 back to BDC. The crankshaft 40 converts piston motion into rotating shaft torque. The crankshaft 40 may be used to drive the alternator. Finally, during the exhaust stroke, the exhaust valve 54 opens to release the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to BDC. It should be noted that the above is shown only as an example, and that the timing of intake and exhaust valve opening and / or closing may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0017] In the presentation of Fig. 1, the controller 12 is a conventional microcomputer including a microprocessor unit 102, input / output (I / O) ports 104, an electronic storage medium for executable programs and calibration values, shown as read-only memory (ROM) 106, a random access memory (RAM) 108, a keep-active memory (KAM) 110, and a conventional data bus.In addition to the signals previously discussed, the controller 12 is shown receiving various signals from sensors coupled to the engine 10, including engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a pedal position sensor 134 coupled to an accelerator pedal 130 for detecting force applied by the vehicle operator 132; an intake manifold absolute pressure (MAP) measurement from pressure sensor 122 coupled to intake manifold 46; a boost pressure measurement from pressure sensor 123; a mass air flow (MAF) measurement from mass air flow sensor 120; a measurement of the throttle position (TP) from a sensor 5 and the temperature at the outlet of an intercooler 166 from a temperature sensor 124. The barometric pressure may also be detected for processing by the controller 12 (sensor not shown).According to a preferred aspect of the present description, the engine position sensor 118 generates a profile ignition pickup signal (PIP). This generates a predetermined number of evenly spaced pulses at each revolution of the crankshaft, from which the engine speed (RPM) can be determined. It should be appreciated that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or 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) drawn into the cylinder. Other sensors, not shown, may also be provided, such as an intake air velocity sensor at the inlet of the intercooler and other sensors.

[0018] Furthermore, the controller 12 may communicate with various actuators, which may include engine actuators such as fuel injectors, an electronically controlled intake air throttle plate, a spark plug, camshafts, etc. Various engine actuators may be controlled to provide or maintain torque requests as specified by the vehicle operator 132. These actuators may adjust certain engine control parameters, including variable cam timing (VCT), air-to-fuel ratio (AFR), alternator load, ignition timing, throttle position, etc. For example, if an increase in pedal position is indicated by a pedal position sensor 134 (e.g., during tip-in), the torque request is increased.

[0019] In response to a tip-in, the controller 12 may increase the opening of the throttle valve 62, thereby increasing the intake airflow. As shown here in the Fig. 2 and Fig. As outlined in Figure 11, the increased airflow available during tip-in can be advantageously used to purge condensate from a CAC to an engine intake. At the same time, spark timing adjustments can be used to maintain torque through combustion phasing during purging.

[0020] In some embodiments, an increase in mass air flow may be triggered by systems other than the vehicle operator, such as in response to a condensate level in the CAC. For example, purging of condensate may be indicated by the CAC, requiring an increase in mass air flow through the CAC. In this case, engine torque must remain unchanged despite the increase in airflow. Here, the engine actuators may be adjusted to maintain the desired torque requirement. For example, torque may be reduced by retarding (retarding) or advancing (advancing) spark timing with respect to MBT to compensate for the (proactive) increase in airflow during the purge routine.In another example, retarding (retarding) or advancing (advancing) the VCT may be used to reduce torque during the proactive purge routine. In some embodiments, adjusting the AFR leaner or richer than RBT (rich for best torque) may reduce power output at the larger throttle opening to help maintain the torque demand. Additionally, increasing the alternator load may provide torque compensation. Vehicles with electric machines (e.g., hybrid vehicles) may be able to increase the alternator load to a greater extent because they may have a wider operating range.

[0021] On Fig. 1, in some examples, a read-only memory 106 as a storage medium may be programmed with computer-readable data representing instructions executable by the microprocessor unit 102 to perform the methods described below, as well as other variations that are expected but not specifically recited. Example methods are described herein with reference to the Fig. 2 - 6 described.

[0022] Now on Fig. Referring to Figure 2, an exemplary method 200 for purging condensate from a CAC during a tip-in or a proactive condensate purge routine while maintaining a desired torque level is shown. The choice may be based on vehicle operating conditions and a CAC condensate level. By performing a purge routine during a tip-in, the increased airflow at tip-in may be used to purge condensate. Under other conditions, the airflow may be actively increased to complete the purge.

[0023] At 202, method 200 includes estimating and / or measuring engine operating conditions. These may include driver torque request (based on pedal position), engine speed (Ne) and load, ECT, boost, ambient temperature, MAF, MAP, EGR amount, air-to-fuel ratio (A / F), ambient humidity, ambient pressure, barometric pressure (BP), engine temperature, exhaust catalyst temperature, CAC conditions (intake and exhaust temperature, intake and exhaust pressure, flow rate through the CAC, etc.), and other parameters. At 204, the routine adjusts one or more engine actuator settings based on the engine operating conditions and the torque request. The adjusted actuator settings may include, for example, variable cam timing (VCT), AFR, throttle opening, spark timing, etc.

[0024] At 206, the method 200 includes determining the condensate height in the CAC. This may include retrieving details such as ambient air temperature, ambient air humidity, intake and outlet charge air temperature, and intake and outlet charge air pressure from a plurality of sensors and using the variables to determine the amount of condensate formed in the CAC. In one example at 208, the condensate heights at the CAC are based on a (in Fig. 3) that calculates the condensate formation rate in the CAC based on ambient temperature, CAC outlet temperature, mass flow, EGR, humidity, etc. In another example, the condensate formation value at 210 is mapped as a function of the CAC outlet temperature and a ratio of CAC pressure to ambient pressure. In an alternative example, the condensate formation value may be mapped as a function of the CAC outlet temperature and engine load. The engine load may be a function of air mass, torque, accelerator pedal position, and throttle position, and thus may provide an indication of the airflow velocity through the CAC. For example, a low engine load combined with a relatively cool CAC outlet temperature may indicate a high condensate formation value due to the cool surfaces of the CAC and the relatively low intake airflow velocity. In one example, the map may include an ambient temperature modifier.In another example, a pressure ratio of the CAC to ambient pressure can be used to estimate condensate formation. The engine load can be normalized and estimated in the intake manifold (behind the throttle), so the pressure may be lower than in the CAC.

[0025] At 212, method 200 determines whether condensate storage in the CAC is increasing. That is, it may be determined whether an amount (or height) of condensate at the CAC is increasing over time. If condensate storage is increasing, the routine includes retarding spark timing during increased condensate storage at 214 to control knock. Method 200 continues from both 212 and 214 to determine whether the CAC condensate height is above a threshold T1 at 216. Threshold T1 may reflect an amount of condensate above which ingestion by the engine may cause misfire events. If the CAC condensate height is not above threshold T1, the routine determines whether the CAC condensate height is in a steady state (e.g., the condensate height is not increasing or is decreasing) at 218.If the CAC condensate height is steady, the routine maintains ignition timing at 220 on MBT. If the CAC condensate height is not steady, the routine ends.

[0026] Returning to 216, if the condensate height is above threshold T1, the routine determines at 222 whether a tip-in condition exists. In one example, a tip-in condition may be inferred based on a throttle change or an air mass change. In another example, a tip-in condition may be inferred based on a vehicle operator applying the accelerator pedal and moving a pedal position beyond a threshold position (or by a threshold amount). As another example, tip-in conditions may be inferred when the vehicle accelerates. If a tip-in exists, at 224, condensate is purged from the CAC to the engine intake manifold during tip-in. Specifically, airflow to the intake manifold is increased based on the change in pedal position to increase torque (as requested by the vehicle operator).Additionally, the routine advances spark timing at 224 during the tip-in induced purge cycle to allow delivery of desired torque while reducing condensate pickup-induced misfires. In an alternative example, the amount of spark retard is limited instead of advancing spark timing.

[0027] If a tip-in condition is not confirmed at 222, the method may perform a proactive condensate purge routine at 226 to purge condensate from the CAC. This may include increasing airflow to the intake manifold (without a corresponding change in pedal position) while maintaining torque to purge condensate. Spark timing may be retarded during the purge cycle at 226 to reduce torque resulting from the increased airflow, thereby enabling maintenance of engine torque during purging. As described in Fig. As outlined in Figure 4, additional conditions that can be assessed before initiating the proactive condensate purge routine include confirming that combustion stability and airflow are within predefined blowdown airflow height ranges. Thus, even if the condensate heights are above the threshold and the airflow is within the blowdown airflow height range, if stable combustion conditions are not met, the proactive CAC purge routine cannot be completed. Details about the proactive purge cycle are described in Fig. 5 and explained further below.

[0028] Fig. Figure 3 shows a method 300 for estimating the amount of condensate stored in a CAC. Based on the amount of condensate at the CAC relative to a threshold, condensate purge routines, such as those for Fig. 2 discussed.

[0029] The method begins at 302 by determining the engine operating conditions. These may include, as at 202, ambient conditions, CAC conditions, air mass, EGR flow, engine speed and load, boost, etc. Next, at 304, the routine determines whether the ambient humidity is known. In one example, the ambient humidity may be known based on the output of a humidity sensor coupled to the engine. If the humidity is unknown (for example, if the engine does not include a humidity sensor), the humidity may be set to 100% at 306. However, if the humidity is known, the known humidity value, as supplied by the humidity sensor, may be used as the humidity setting at 308.

[0030] Ambient temperature and humidity can be used to determine the dew point of the intake air, which can be further influenced by the amount of EGR in the intake air (for example, EGR may have a different humidity and temperature than the air from the atmosphere). The difference between the dew point and the CAC outlet temperature indicates whether condensation will form in the cooler, and the air mass can influence how much condensation actually accumulates in the cooler. At 310, an algorithm may calculate the saturated vapor pressure at the CAC outlet as a function of the CAC outlet temperature and pressure. Then, at 312, the algorithm calculates the water mass at that saturated vapor pressure. Finally, at 314, the condensation formation rate at the CAC outlet is determined by subtracting the water mass under the saturated vapor pressure condition at the CAC outlet from the water mass in the ambient air.By determining the time between condensate measurements at 316, method 300 may determine the amount of condensate in the CAC since the last measurement at 318. The time between measurements may be based on engine operating conditions or weather conditions. For example, if conditions are present that increase condensate formation, such as rain, the time between measurements may be shortened to better track condensate formation. In another example, the time between condensate measurements may be shorter if the condensate height in the CAC approaches the threshold height for condensate purge. Alternatively, the time between measurements at 316 may be lengthened if the condensate height in the CAC is lower or if condensate formation conditions (such as high humidity) are not present. In still other embodiments, the measurements may be taken at fixed, predetermined intervals.In one example, an estimate of condensate formation as a proportion of the air mass rate would be sampled much faster than actual conditions could change. Even at a rate of 0.5 s per sample, an adequate estimate can be made for tracking condensate at altitudes that could affect combustion upon condensate pickup. The current amount of condensate in the CAC is calculated at 322 by adding the condensate value estimated at 318 to the previous condensate value and then subtracting any condensate losses since the last routine (i.e., any amount of condensate removed by purge routines, for example) at 320. Condensate losses can be assumed to be zero if the CAC outlet temperature was above the dew point. Alternatively, condensate losses above the dew point can be tracked by evaporation.

[0031] In addition to determining the amount of condensate in the CAC, method 300 may be used to determine the condensate flow from the CAC to the engine intake manifold. For example, the CAC may exist in three different states. In a first state, the CAC may store condensate, so that the condensate height (determined at 322) increases. For example, if the condensate amount at 318 or the condensate formation rate at 314 has a positive value, the condensate height in the CAC may be considered increasing. In doing so, water may be removed from air circulating through the CAC and stored at the CAC. Thus, under such conditions, due to the removal of water from the circulating air, the humidity entering the intake manifold (after passing through the CAC) may be lower than the humidity of the ambient air (entering the CAC).

[0032] In a second state, the CAC may release condensate from the CAC to the engine intake manifold (e.g., purge), causing the condensate height to decrease. For example, if the condensate amount at 318 or the condensation formation rate at 314 has a negative value, the condensate height in the CAC may be considered to be decreasing. In this case, water already stored in the CAC may be released into the intake manifold. Under such conditions, due to the removal of water from the CAC, the humidity entering the intake manifold (after passing through the CAC) may be higher than the humidity of the ambient air (entering the CAC). In this case, the release may occur either due to air mass velocity or evaporation.The reduction in stored condensate, or condensate removal, can occur as a function of the air mass flow rate when the flow rate is above a threshold, with the rate of reduction being relatively linear with the air flow. Thus, the evaporative component of water removal occurs at a much lower rate and would only be considered in determining condensate storage reduction under long steady-state conditions when no condensate is formed.

[0033] In a third state, the CAC may be in a steady state where the condensate head in the CAC is essentially constant (i.e., neither increasing nor decreasing). For example, when the condensate amount at 318 or the condensation formation rate at 314 is at or around zero, the condensate head may be considered to be in a steady state. During the steady state, the intake manifold humidity may be essentially equal to the ambient humidity.

[0034] Now on Fig. Referring to Figure 4, a method 400 for determining whether a proactive CAC purge procedure can be performed is set forth. Specifically, method 400 confirms whether conditions exist to activate a proactive CAC purge routine (where airflow through the CAC is actively increased without a corresponding increase in torque) without inducing misfires during water intake.

[0035] Method 400 includes determining at 402 whether engine operating conditions are met to activate the purge routine. These may include, for example, operating requirements for stable combustion conditions. Operating requirements for stable combustion may include, for example, the engine coolant temperature being above a threshold, spark retard being within a threshold, VCT not being retarded more than a threshold, EGR level being below a threshold, and fuel quality being within a predetermined level. If these conditions are not met, a proactive CAC purge routine may not be performed because combustion stability could be impacted.In response to the conditions not being met, the routine proceeds to 408 where several steps are performed to enable purging of CAC condensate without performing a proactive drain routine.

[0036] As an example, at 410, the engine control unit may take measures to reduce condensate formation at the CAC, such as by adjusting the CAC efficiency. The CAC efficiency may be adjusted (e.g., reduced) through the use of a grille shutter system or a cooling fan. For example, the opening of the grille shutters may be reduced to reduce external cooling airflow through the CAC and reduce the CAC efficiency.

[0037] In another example, at 412, the controller may adjust one or more engine operating parameters or actuators to improve or increase engine combustion stability. For example, during condensate pickup, an amount of spark retard used may be reduced or limited. After improving combustion stability, the routine may Fig. 4 so that a CAC purge routine can be performed while combustion stability is within a threshold.

[0038] In yet another example, at 414, control may wait until the conditions for proactive CAC purge (as previously set forth at 402) are met. That is, the proactive condensate purge routine may be delayed until the selected engine conditions of 402 are met. Alternatively, if the purge routine was not initiated due to airflow conditions not being met (i.e., the airflow is not within a threshold range at 406), then control may wait and delay the CAC purge routine until the airflow conditions are met (i.e., until the airflow is within the threshold range).

[0039] The controller may select one of the alternative options (410-414) shown at 408 based at least on the amount of condensate within the CAC. For example, if a larger amount (e.g., more than a threshold amount) of condensate has built up in the CAC, or the condensate buildup rate is higher (e.g., more than a threshold rate), a purge procedure may need to be performed sooner. In this case, the system may choose to actively adjust the engine operating conditions rather than delaying initiation of the purge routine until the conditions are met on their own. In some examples, the routine may employ multiple options 410-414.For example, at 408, the controller may take one or more alternative actions to reduce condensate formation (such as grille shutter settings that reduce CAC efficiency and thereby reduce condensate formation at the CAC) along with adjusting engine operating conditions to increase combustion stability.

[0040] Returning to 402, if the engine conditions for activating a purge routine are met, the routine determines the appropriate condensate thresholds (T1) and airflow thresholds (T2 and T3) at 404. If condensate buildup in the CAC is above a first threshold T1, the need for a CAC purge routine may be indicated. The first (condensate) threshold T1 may vary depending on vehicle operating conditions, including, for example, a combustion rate, engine temperature, and spark timing. In some situations, when engine combustion rates are faster, the engine may tolerate blowing off a larger amount of condensate from the CAC. Therefore, the first (condensate) threshold T1 may be set to a higher value when combustion rates are higher and / or engine temperatures are higher.Conversely, when combustion rates are slower and / or engine temperatures are lower, the first (condensate) threshold T1 may be set to a lower value. In another example, the first (condensate) threshold T1 may be decreased as spark retard increases. Thus, the first (condensate) threshold T1 may have a higher value when spark timing is not retarded and a lower value when spark timing is retarded. By adjusting the condensate threshold based on spark timing, condensate blowoff misfire events may be reduced. In one example, the condensate pickup rate as a function of air mass flow rate may be the main (e.g., dominant) factor unless the threshold level is low enough that no pickup rate causes misfire.Likewise, the ignition timing can be adjusted as a function of the intake rate or based on feedback from an intake oxygen sensor.

[0041] The airflow thresholds T2 and T3 can also be set at 404 so that the airflow flowing through the CAC and into the engine intake is within a range of a blowoff airflow amount. The blowoff airflow amount can be defined as the amount of airflow required to flush a certain amount of condensate from the CAC during the purge procedure. Therefore, at 404, the routine determines both the blowoff airflow amount as a function of the amount of condensate in the CAC and the airflow thresholds for activating purge. For example, the airflow threshold can be defined such that: |Airflow - T2| < T3. In this equation, T2 can be the blowoff airflow amount, the airflow is the current airflow flowing through the CAC and into the intake manifold, and T3 is a set airflow threshold.In other words, a purge routine can only be initiated if the airflow through the CAC is less than the set airflow threshold T3 above or below the blowoff airflow height T2. This means that the airflow may need to be within a range defined by the threshold T2 - T3 at the low end and the threshold T2 + T3 at the high end. In this way, airflow is controlled by the controller during a purge cycle so that condensate blowoff can be controlled. The blowoff can be zero below the threshold and one percent of the air mass if the air mass increases above the minimum threshold. This allows the blowoff to be carried out slowly and reduces the likelihood of engine misfires or degradation of engine performance.The airflow threshold T3 can be adjusted to maintain combustion stability throughout the purge procedure. Alternatively, a threshold intake rate can be set instead of a total amount. The intake rate can then be controlled by controlling the airflow rate (for example, by curtailing the air mass flow rate until condensate is purged). To maintain combustion stability, the parameters that are changed to maintain the torque demand throughout the purge procedure may need to remain within certain thresholds. These parameters can include ignition timing, alternator load, VCT, and AFR. Therefore, T3 should be adjusted so that these parameters are not increased or decreased outside their combustion stability thresholds.For example, the threshold T3 can be set so that ignition retardation is not increased above a level that can lead to combustion instability.

[0042] After all condensate and airflow thresholds have been determined, method 400 verifies at 406 whether the current condensate and airflow heights are within these thresholds. For example, the routine checks whether the condensate height, as determined in method 300, is above threshold T1. The routine may also check whether the airflow is within the threshold range, that is, |Airflow - T2| < T3. If these two conditions are met, the routine proceeds to 416, where the CAC purge routine is initiated. Details of this purge routine are described in Fig. 5 and discussed further below. However, if the conditions at 406 are not met, the routine returns to 408, where one or more actions are taken, as discussed above. For example, the routine may include waiting at 414 until airflow is within the specified threshold.

[0043] Fig. 5 shows a method 500 for performing a proactive CAC purge routine. The method 500 may be executed by the controller 12 according to instructions stored therein. The method 500 includes, at 502, determining the airflow increase required to blow off the condensate in the CAC. This may be determined based on the amount of condensate in the CAC calculated by the method 300 and the corresponding blow-off airflow height (threshold T2, as described with reference to Fig. 4 discussed above). The method proceeds to 504 to determine the torque offset required for the airflow increase determined at 502. Thus, a torque offset is required here because the airflow increase is not due to a change in pedal position or a request for increased torque from the vehicle operator. Rather, the airflow increase is for blowing condensate from the CAC into the engine. Thus, as the airflow height increases, a larger torque offset may be required to allow overall engine torque to be maintained. At 506, control increases airflow through the CAC by the specified amount while simultaneously adjusting one or more engine actuators to maintain engine torque.Airflow through the CAC can be increased by increasing air mass via an intake throttle and retarding spark advance to maintain torque delivery. In one example, increasing airflow via the intake throttle increases airflow to the engine's intake manifold. Thus, by adjusting the engine actuators while increasing airflow, overall torque can be reduced so that an actual torque demand can be maintained during the condensate purge cycle.

[0044] Adjusting the engine actuators to maintain torque may include adjusting the alternator load at 508. By increasing the alternator load applied to the engine, torque may be reduced, thereby compensating for the increased engine airflow. An alternator load applied to the engine may be increased by adjusting an alternator coil current. Adjusting the actuators may also include adjusting spark retard at 510. In one example, increasing the amount of spark retard (i.e., retarding the spark further away from MBT) may reduce torque and help maintain the desired torque request. Alternatively, at 512, adjusting the actuators may include adjusting the VCT. In some embodiments, retarding the VCT may reduce torque, thereby compensating for the increase in engine airflow.In yet another example, adjusting the actuators may include adjusting the air-fuel ratio (AFR) at 514. Specifically, fuel leaning may be used to increase AFR, thereby reducing power output at a larger throttle opening. Thus, in one example, increasing AFR may offset the increased airflow entering the engine's intake manifold and help maintain torque.

[0045] In some embodiments, a combination of the above parameters may be adjusted to compensate for the airflow increase and maintain torque. In other embodiments, a priority hierarchy may be employed for these adjustment parameters based on their impact on combustion stability. For example, increasing alternator load may not increase combustion instability to the same extent as would be the case with VCT or spark timing adjustments. Thus, the priority hierarchy at 506 may include first adjusting alternator load and then (if further torque reduction is needed) continuing with adjusting spark timing, VCT, and / or AFR. In some embodiments, a trigger may be set to advance to the next parameter in the hierarchy.For example, initially, the alternator load may be used to reduce torque, and once maximum alternator load has been applied to the engine, the trigger may be set to accomplish the remaining torque reduction using VCT, spark timing, or AFR adjustments. The priority order may also be changed depending on engine operating conditions and other vehicle operating conditions, such as vehicle speed, a vehicle operating mode, a battery state of charge, etc. Example actuator adjustments performed during a proactive purge routine are described herein with reference to FIG. Fig. 7 - 8.

[0046] After making all adjustments to activate the CAC purge routine at 506, method 500 checks the condensate level relative to a threshold T4 at 516. If the amount of condensate in the CAC has been sufficiently purged and is less than T4, the purge cycle ends at 520, and all engine actuators and parameters are returned to their original settings (or to corrected settings based on the current torque demand). These parameters may include airflow, spark timing, VCT, throttle position, AFR, and alternator load. However, if the amount of condensate in the CAC is not below the threshold T4, the purge cycle continues to purge condensate from the CAC at 518.

[0047] In another embodiment, rather than ending the purge routine based on the condensate level in the CAC, the purge routine may be terminated based on the elapse of a threshold duration since initiation of the purge routine. For example, at 506, a timer may be started when the purge routine is initiated, and a signal to terminate the purge cycle may be set at 516 in response to a set duration of time elapsed on the timer. The threshold duration monitored on the timer (also referred to herein as the cycle time) may be set based on engine operating conditions and the amount of condensate in the CAC. In particular, in one example, a longer threshold duration may be allowed to elapse in response to a larger amount of condensate in the CAC.

[0048] Thus, introducing wastewater into the engine during condensate purge (e.g., purge during a tip-in or purge during a proactive purge routine) from a CAC may increase the likelihood of misfire events. In one example, this may be addressed by adjusting the ignition timing during condensate purge (the purge cycle) and / or during condensate storage. As described herein with reference to Fig. As outlined in Figure 6, an initial boundary knock limit may be set based on ambient humidity. The initial boundary setting may also include an initial amount of MBT retardation. Condensate flow from the CAC (during storage and purge) may change the intake manifold humidity relative to the ambient humidity. Thus, the intake manifold humidity and CAC condensate flow state can be used to modify these initial settings to reduce engine misfire events and maintain torque during condensate purge.

[0049] Now on Fig. 6, an example method 600 is shown for adjusting a boundary knock limit and spark timing based on ambient humidity and the condensate storage height in the CAC. The method 600 includes, at 602, determining engine intake manifold humidity. In one example, intake manifold humidity may be accurately determined using an engine intake manifold oxygen sensor. In another example, humidity may be determined by a UEGO located downstream of the catalyst during a deceleration fuel shut-off (DFSO) event. However, this device may not be able to respond quickly enough to make spark adjustments upon ingestion of the condensate. In yet another example, intake humidity may be determined based on engine operating conditions, the condensate storage height in the CAC, and the condensate flow (e.g., amount, flow rate, etc.).) from the CAC (as previously determined in method 300). At 604, the intake manifold humidity is compared to the ambient humidity. If at 604, the intake manifold humidity is greater than the ambient humidity, the routine advances the boundary knock limit at 606. In particular, the knock limit may be advanced to take advantage of the knock reduction effect of increased engine humidity. The routine then advances spark timing to MBT or to the corrected boundary knock limit during condensate purge (that is, during the reduction of condensate height in the CAC). For example, during a condensate purge cycle due to tip-in, when condensate is purged to the engine intake, the intake manifold humidity may be greater than the ambient humidity.Under such conditions, spark timing may be advanced past the initial boundary knock limit setting toward the MBT or to the new boundary knock limit. The amount of advance may be adjusted to maintain engine torque throughout the condensate purge cycle. The amount of advance may be based, for example, on pedal position, engine speed, and / or throttle position. Torque reduction from advance is then determined as a function of how far the spark timing is retarded from the MBT spark timing. In addition, or alternatively, closed-loop feedback from crankshaft acceleration may be used to advance spark timing when combustion rates are slow and limit advance based on boundary feedback from the knock sensor.

[0050] If at 604 the intake manifold humidity is not greater than the ambient humidity, then at 610 it is determined whether the intake manifold humidity is less than the ambient humidity. If so, the routine retards the boundary knock limit at 612. In particular, the knock limit may be retarded to compensate for the effect of a decrease in humidity during engine knock. Then, the routine retards the spark timing during condensate storage (that is, during the increase in condensate height in the CAC) to the corrected boundary knock limit. During periods of increasing condensate height (storage) at the CAC, for example, the spark timing may be retarded from the initial amount of spark retard to a greater final amount of spark retard. The amount of spark retard may be adjusted to maintain engine torque during condensate storage.

[0051] If the intake manifold humidity is not below ambient humidity at 610, then a determination may be made at 616 whether the intake manifold humidity is substantially equal to the ambient humidity. Thus, at steady-state condensate levels at the CAC where the condensate levels are neither increasing nor decreasing but remain substantially the same, the intake manifold humidity may be substantially equal to the ambient humidity. If the intake manifold humidity is substantially equal to the ambient humidity, the routine maintains the initial boundary knock limit at 618. Then, at 620, the spark timing is maintained at the boundary knock limit during the steady-state condensate levels at the CAC. After performing all boundary knock limit and spark timing adjustments, the routine ends.

[0052] Fig. Figure 7 shows a graphical example of a proactive CAC emptying routine that uses the previously described Fig. 2-5 are used. Curve 700 shows an example of engine airflow in plot 702, spark timing in plot 704, throttle opening in plot 706, variable cam timing (VCT) in plot 708, charge air cooler condensate height (CAC CL) in plot 710, pedal position (PP) in plot 712, and engine torque in plot 714 as a function of time (along the x-axis). In this example, engine airflow is increased in response to CAC condensate height, initiating a purge (purge) procedure that includes adjusting spark timing to maintain torque.

[0053] Before t1, CAC condensate height (CAC CL) increases (710) while PP (712), torque (714), VCT (708), throttle opening (706), spark timing (704), and engine airflow (702) remain relatively constant. At time t1, the vehicle accelerates in response to a tip-in, as shown by an increase in pedal position (712). Consequently, to meet the increased torque demand, throttle opening increases (706), thereby increasing engine airflow (702) and torque (714). At time t2, engine airflow (702) increases above threshold T2, which corresponds to the CAC blowoff airflow height (i.e., an airflow height above which CAC condensate can be blown off into the engine intake). Thus, at t2, the CAC condensate height (710) begins to decrease at a rate R1 until time t3 when the engine air flow decreases below T2.This first example of condensate blowdown during a tip-in (shown at 716) does not cause engine misfires because the condensate amount is lower (below threshold level T1). Thus, threshold level T1 may correspond to a condensate level that triggers a proactive drain cycle.

[0054] It will be appreciated that in an alternative embodiment, the rate at which the condensate height decreases (R1) may be a factor in misfire control. However, if the total condensate amount is small enough, the rate of decrease may not be a factor in misfire control. Thus, to control the intake rate, the rate of change of airflow can be slowed via throttle adjustments. However, this may result in the vehicle driver experiencing a real and perceived difference in performance / acceleration. If the vehicle is a hybrid application, it will be understood that the electric motor torque can be used to generate or deliver all of the torque requested by the driver by controlling the rate of change of airflow or condensate entering the internal combustion engine.In this case, the hybrid's electric motor would output torque instead of absorbing torque (which can be used for proactive purging to increase engine airflow).

[0055] After time t3, the CAC condensate height begins to increase again with increasing time in example 700 until time t4, when it reaches the threshold height T1 (710). At this time, the engine airflow is between the lower threshold T5 and the upper threshold T2, such that |Airflow - T2|< T3 (702). In this example, T3 is the difference between the condensate blowdown height T2 and the airflow threshold T5. Since the engine airflow is within the set threshold range (i.e., below the upper threshold T2 but above the lower threshold T5) and the condensate height in the CAC is above the threshold T1, a proactive CAC purge routine is triggered. Accordingly, a throttle opening is increased at t4 (706), thereby increasing engine airflow above threshold T2 (702).At the same time, the controller increases the spark retard amount by a larger amount ΔS1 (704) to maintain the torque request throughout the purge procedure (714). The condensate head in the CAC begins to slowly decrease at a rate R2 (710). During this second condensate purge with a proactive routine (shown at 718), the purge rate R2 is less than the purge rate R1 (during the previous purge at 716) because the engine airflow is at a lower altitude (L2 at 718 vs. L1 at 716). The engine airflow (702), spark timing (704), and torque (714) are held stable until time t5, when the condensate head in the CAC decreases to the threshold height T4 (710). This terminates the purge procedure and returns all parameters to their previous or currently requested settings.

[0056] On Fig. 7, the CAC purge procedure initiated at time t4 (shown at 718) could proceed in various ways depending on the engine operating conditions. In the example shown, torque compensation is achieved by adjusting only a single engine operating parameter, specifically, by increasing the spark retard amount alone (704). By retarding the spark timing, the torque remains constant despite increasing airflow. Thus, the vehicle operator is not aware of any change in vehicle performance, and drivability is not affected. However, in other examples, torque compensation may be achieved by adjusting a combination of different engine actuators, as previously discussed at Fig. 5 (at 506). These actuators can adjust engine controls such as alternator load, ignition timing, VCT, and AFR. In particular, several of these parameters can be adjusted at once to maintain the torque demand during the purge routine. An example of such a purge routine is described in Fig. 8 shown.

[0057] Fig. 8 shows an alternative graphical example 800 for the Fig. 2-5. Curve 800 again shows an example of the engine airflow in plot 802, the ignition timing in plot 804, the throttle opening in plot 806, the variable camshaft timing (VCT) in plot 808, the charge air cooler condensate height (CAC CL) in plot 810, the pedal position (PP) in plot 812, and the engine torque in plot 814 as a function of time. The engine airflow increases in response to the CAC condensate height, triggering a purge procedure that includes adjusting the ignition timing and VCT to maintain torque.

[0058] Graphical example 800 proceeds in the same manner as graphical example 700 until time t4. At t4, the condensate height in the CAC reaches threshold T1 (810), and the airflow height is between T5 and T2 (802). As a result, the CAC purge procedure is initiated. The throttle opening is increased at t4 (806), increasing engine airflow above T2 (802). At the same time, the controller adjusts a combination of parameters to maintain torque throughout the purge procedure.

[0059] In contrast to example 700, in which only spark timing is adjusted, in example 800, control adjusts both spark timing and VCT. At time t4, spark timing is retarded (804) by a lesser amount ΔS2 (which is less than the retard ΔS1 applied in example 700). Since VCT is also retarded in example 800 (see plot 808), spark timing may be retarded to a lesser extent here. That is, by using concurrent VCT adjustments, an amount of spark retard applied during the purge routine may be reduced. In yet other examples, an increase in alternator load and / or AFR may be implemented in addition to, or in combination with, these parameters to maintain torque.At time t5, the emptying procedure ends and all parameters are returned to their previous or currently requested settings.

[0060] Fig. 9 shows a graphical example of a method 600 for adjusting a boundary knock limit and spark timing based on ambient humidity and condensate height in a CAC. The example graph 900 illustrates boundary knock limit adjustments at 904, spark timing at plot 902, changes in engine intake manifold humidity at plot 906, and CAC condensate height at plot 910.

[0061] Prior to time t1, condensate may be stored at the CAC. Due to the continued removal of water from the intake air into the charge air cooler, the intake manifold humidity (906) is less than the ambient humidity (908). During this time, the CAC operates in a first state where the condensate height increases (910), indicating the storage of condensate in the CAC. In response to the intake manifold humidity being less than the ambient humidity, the boundary knock limit may be retarded (904) to compensate for the increased knock effect that may result from the lower intake manifold humidity. Furthermore, during this first state, spark timing is retarded from MBT to the corrected boundary knock limit.

[0062] At time t1, the height of condensate stored at the CAC may rise above a threshold. In response to pedal tip-in, CAC purging may be performed. Due to the continued removal of water from the charge air cooler into the engine intake, intake manifold humidity (906) increases above ambient humidity (908). The intake manifold humidity remains higher than ambient humidity until time t2. During this time, the CAC operates in a second state where the condensate height decreases due to a purge (CAC purge) cycle (910). In response to the intake manifold humidity being higher than ambient humidity, the boundary knock limit may be advanced (904) to take advantage of the knock reduction effect that may result from the higher intake manifold humidity. Furthermore, in response to condensate purging, the controller advances spark timing to MBT.

[0063] After time t2, the intake manifold humidity (906) may be substantially at or near ambient humidity (908). Accordingly, the boundary knock limit is returned to MBT (904). Here, the CAC may operate in a third state after time t2 in which the condensate height is in a steady state (910). During this third state, the controller maintains spark timing at MBT (902).

[0064] In this way, boundary knock limits and spark timing can be retarded during condensate storage at the CAC, while boundary knock limits and spark timing can be advanced during condensate discharge from a CAC. By adjusting the boundary knock limit and spark timing in response to water ingestion from a CAC, engine misfire events and torque loss caused by water ingestion can be reduced.

[0065] Now on the Fig. 10 and Fig. Referring to Figure 11, two graphical examples of ignition timing adjustment in response to purging condensate from an intercooler are shown for two different driving conditions. Fig. 10, condensate is purged from a CAC during a proactive purge cycle. This purge cycle is initiated in response to a condensate level in a CAC while maintaining pedal position below a threshold (i.e., not in a tip-in state). Plot 1000 shows pedal position (PP) in plot 1002, airflow to the intake manifold (Airflow) in plot 1004, condensate purge in plot 1006, and ignition timing (Firing) in plot 1008.

[0066] For example, prior to t1, condensate purge cannot be performed because the condensate head at the CAC is below a threshold amount. At time t1, a condensate purge routine is initiated in response to the condensate head increasing above the threshold. Specifically, a proactive purge routine is initiated. Accordingly, to purge the condensate, airflow to the intake manifold is increased (e.g., above a blowoff airflow head), as shown at plot 1004. Here, the airflow increase is responsive to the condensate head in the CAC. That is, airflow is increased even though pedal position remains below a threshold (1002) and no request for increased torque is received from the vehicle operator. The increase in airflow activates the purging of condensate from the CAC (1006).Because condensate purge is triggered by a controlled process (process 400) based on the condensate head and airflow thresholds, a smaller amount of condensate is purged per engine cycle, and further, purging is performed for a longer duration. In response to the extended condensate purge with a lower purge rate (i.e., a smaller amount purged per cycle), spark timing is retarded from MBT (1008). Spark retard is used to keep engine torque constant. At time t2, the condensate purge cycle ends due to the condensate head returning below a threshold. Accordingly, at t2, airflow is reduced and returned to the original settings (1004), ending condensate purge (1006). Spark timing is also returned to MBT (1008).

[0067] With reference to Fig.11, condensate is purged from a CAC during a tip-in, represented by an increase in pedal position. Condensate is purged from the CAC in response to an increase in airflow to the intake manifold caused by a tip-in. Plot 1100 shows the pedal position in plot 1102, the airflow to the intake manifold (airflow) in plot 1104, the condensate purge in plot 1106, and the ignition timing (spark) in plot 1108.

[0068] Condensate purge cannot be performed before t1; for example, the condensate height at the CAC is less than a threshold amount. At time t1, airflow to the intake manifold increases in response to the pedal position exceeding a threshold, indicating a tip-in (1102), above a blowoff airflow height (1104). Increasing airflow then purges the condensate from the CAC (1106). Because condensate purge is triggered by a tip-in, a larger amount of condensate is purged per cycle over a shorter duration. In response to the accelerated condensate purge at a higher purge rate (i.e., a higher purge amount per cycle), spark timing is advanced toward MBT (1108). Here, spark advance is used to reduce the likelihood of misfires and increase engine torque. At time t2, the pedal position decreases (1102), terminating the tip-in.Airflow is returned to an original, lower height, reducing condensate purge (1106). Ignition timing is also returned to its previous degree of spark retardation (1108).

[0069] In this way, condensate from a CAC may be purged into an intake manifold while spark timing is adjusted based on the amount of condensate purged per cycle. The amount of condensate purged per cycle may be based on ambient and engine operating conditions, including ambient temperature, ambient humidity, intake air EGR content, mass air flow, and CAC outlet temperature. The amount of condensate purged per cycle may be further based on pedal position. For example, the amount of condensate purged per cycle may increase when a pedal position exceeds a threshold position (for example, during tip-in) and a mass air flow rate increases. Spark timing may be advanced or retarded based on the type of purge, for example, based on whether the purge is based during tip-in as opposed to proactive purge.In the tip-in example, if the amount of condensate purged per cycle is greater (e.g., greater than a threshold), the spark timing may be advanced. The amount of advance may be based on a pedal position (e.g., the tip-in degree) and a vehicle driver torque request. As another example, the amount of advance may be changed from a baseline value based on the estimated condensate pickup rate or the measured condensate pickup rate (e.g., as determined based on an intake oxygen sensor). Here, feedback from the intake oxygen sensor may provide an estimate of the amount of water in the intake.In another example, such as during proactive CAC purge, where the amount of condensate purged per cycle is lower (e.g., below the threshold), spark timing may be retarded to keep engine torque constant while increasing airflow.

[0070] As described above, condensate can be purged from a CAC by increasing airflow to the engine intake manifold. Airflow can be increased to a condensate blowoff height in response to a driver-initiated tip-in or a periodic proactive condensate purge cycle. During condensate purge, engine actuators may need to be adjusted to maintain the torque demand. Engine actuator adjustments may include adjusting spark timing, VCT, alternator load, and AFR ratio. By adjusting engine actuators to maintain the torque demand, an increase in airflow to purge the CAC may go unnoticed by the vehicle operator. Spark timing adjustments can also be based on condensate height in the CAC, intake manifold humidity, ambient humidity, and condensate flow from the CAC.In particular, the amount of pre-ignition can be increased when a CAC is purged during tip-in to compensate for the higher humidity that can slow the combustion rate and reduce the risk of knock. By increasing the amount of pre-ignition, combustion stability is improved and the risk of misfires is reduced. Calculations of the amount of condensate in the CAC can also be used to determine when a purge cycle is required. When all engine operating conditions and engine airflow thresholds are met, a purge cycle can be initiated. In this way, performing periodic condensate purge cycles can help prevent the ingestion of large amounts of condensate at once and cause engine misfires. By using techniques to adjust the ignition timing during periods of condensate storage and purge, engine misfires can be reduced.

[0071] One of ordinary skill in the art will appreciate that the routines described herein may represent one or more of any number of CAC purge procedures using various motor actuator controls. Thus, various illustrated steps or functions may be performed in the order illustrated, in parallel, or in some cases omitted. Likewise, the control sequence is not necessarily required to achieve the objectives, features, and advantages described herein, but is provided for convenience of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be performed repeatedly depending on the particular strategy employed.

[0072] The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts and / or properties disclosed herein, as well as any equivalents thereof.

Claims

[1] A method for an engine (10) comprising: in response to a condensate level in a charge air cooler (166), increasing engine airflow more than requested by a vehicle operator (132) without increasing engine torque by adjusting an engine actuator to maintain torque. [2] The method of claim 1, wherein boosting engine airflow occurs in response to the condensate height in the charge air cooler (166) being greater than a condensate threshold height and an engine airflow being within a blow-off airflow threshold amount, and wherein engine torque is boosted by no more than a desired torque. [3] The method of claim 1, wherein increasing engine airflow comprises increasing the opening of an intake throttle valve (62). [4] The method of claim 1, wherein the condensate height is estimated based on air mass flow, ambient temperature, charge air cooler outlet temperature, charge air cooler pressure, ambient pressure and an EGR amount. [5] The method of claim 4, wherein the condensate height is further corrected based on input from a humidity sensor. [6] The method of claim 1, wherein the condensate height is estimated based on the charge air cooler outlet temperature and the ratio between charge air cooler pressure and ambient pressure and / or the engine load. [7] A method for an engine, comprising: Increasing engine airflow from an initial height while maintaining a pedal position in response to a condensate height in a charge air cooler (166) being higher than a threshold height (T1) and the initial airflow height being below a blow-off height. [8] The method of claim 7, further comprising maintaining torque during airflow enhancement by adjusting spark retard, variable camshaft timing, alternator load, and / or air-fuel ratio. [9] The method of claim 7, wherein the condensate height is estimated based on air mass flow, ambient temperature, charge air cooler outlet temperature, charge air cooler pressure, ambient pressure and an EGR amount. [10] The method of claim 9, wherein the condensate height is further corrected based on input from an ambient humidity sensor. [11] The method of claim 7, wherein the condensate height is estimated based on the charge air cooler outlet temperature and the ratio between charge air cooler pressure and ambient pressure and / or the engine load. [12] The method of claim 7, wherein an amount of boosting the engine airflow is based on a difference between the initial engine airflow height and the blow-off height, and wherein boosting the engine airflow comprises boosting the engine airflow above the blow-off height. [13] The method of claim 7, wherein the condensate threshold height is adjusted based on engine operating conditions. [14] The method of claim 13, wherein the condensate threshold height is increased with increasing engine temperature. [15] The method of claim 13, wherein the condensate threshold height is increased with decreasing ignition retard. [16] The method of claim 7, further comprising reducing an amount of EGR while increasing the airflow. [17] The method of claim 7, wherein the initial airflow height below a blow-off height comprises the initial airflow height within an airflow threshold range. [18] Engine system comprising: an engine (10) having an intake manifold (46); a compressor (162) coupled to the intake manifold (46) upstream of an intake throttle valve (62); a charge air cooler (166) coupled downstream of the compressor (162), an accelerator pedal (130) for receiving a torque request from a driver (132); and a controller (12) with computer-readable instructions therefor, while maintaining an accelerator pedal position, in response to an amount of condensate stored in the charge air cooler (166) which is greater than a threshold value, increasing an opening of the intake throttle valve (62) to increase airflow to the intake manifold (46) by more than requested by the driver (132) while maintaining engine torque. [19] The system of claim 18, wherein maintaining engine torque comprises retarding spark timing, adjusting variable camshaft timing, increasing an alternator load applied to the engine (10), and / or leaning an exhaust air-fuel ratio from stoichiometric. [20] The system of claim 19, wherein increasing the airflow comprises increasing the airflow from an initial setting to a blow-off setting, the blow-off setting being based on the amount of condensate stored in the charge air cooler (166).

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