Method for controlling the intake and exhaust cam phaser in an internal combustion engine to adjust the valve overlap

Abstract

A method for controlling the intake and exhaust cam phaser (148, 150) in an internal combustion engine (102) to adjust the valve overlap, comprising the following steps: sensing an engine speed and engine load of the internal combustion engine (102), Detecting the coolant temperature in the internal combustion engine (102), sensing the relative humidity of the air supplied to the combustion engine (102), using the engine speed, engine load, and humidity in a lookup table to determine the minimum and maximum intake cam phase limit values ​​and the minimum and maximum exhaust cam phase limit values, and advancing the maximum exhaust cam phasing and retarding the maximum intake cam phasing based on coolant temperature as relative humidity increases, thereby reducing valve overlap.

Description

INTRODUCTION

[0001] The present disclosure relates to camshaft phasing and, more particularly, to a method for controlling the intake and exhaust cam phasers in an internal combustion engine to adjust valve overlap.

[0002] From US 2005 / 0211 209 A1 it is known to adjust the intake and exhaust valves of an internal combustion engine based on the engine load, the engine speed and the relative humidity.

[0003] For decades, internal combustion engines, particularly those used in passenger cars and light trucks, have used fixed valve timing. In such engines, the intake and exhaust valves open and close simultaneously with respect to crankshaft rotation and piston positions, regardless of engine speed, load, fuel mixture, ignition timing, or other operating parameters. This occurred despite the fact that fixed valve timing was increasingly recognized as a compromise, generally between low-speed and high-speed operation.

[0004] In response to this confirmation, variable valve timing, or phasing of the intake and exhaust valves of an internal combustion engine, has been used by engine designers and manufacturers as a control method that provides improved engine performance, including improved power and torque, increased fuel efficiency, and reduced emissions. Depending on engineering objectives and other criteria, variable valve phasing may include phasing of intake valve opening and closing, exhaust valve opening and closing, intake and exhaust valve lift, and combinations thereof.

[0005] When the decision is made to incorporate variable valve phasing into a specific internal combustion engine configuration, not only are the preceding aspects of valve phasing addressed, but the engine operating parameters are also addressed to provide the control parameters for such valve phasing. Typical operating parameters monitored in real time to provide control inputs for the valve phasing system are engine speed, engine load, throttle position, and airflow.

[0006] As performance, fuel efficiency, and emissions standards become increasingly demanding, significant effort has been devoted to the continued development of variable valve phasing systems, and the following disclosure is a result of such efforts. SUMMARY

[0007] The present invention provides a method for controlling the intake and exhaust cam adjuster in an internal combustion engine to adjust the valve overlap, the method being characterized by the features of claim 1.

[0008] Under certain higher humidity conditions, maintaining good combustion stability and thus overall engine operation requires reducing intake and exhaust valve overlap by adjusting the phasing of the intake and exhaust camshafts. This is achieved by using a set of cam position reference values ​​and constraints based on engine speed, engine load, and humidity, contained in lookup tables that adjust and limit cam position and valve overlap. To maintain optimal engine performance, intake and exhaust valve overlap is generally reduced at higher ambient humidity, and vice versa. These cam position constraints can be tuned to optimize engine performance, maintain combustion stability, or maximize other operating objectives.If the sensed ambient humidity is below a predetermined humidity threshold such that no restrictions on intake and exhaust cam position are required, no such restrictions are imposed.

[0009] Thus, it is an aspect of the present disclosure to provide a method for controlling an internal combustion engine that optimizes performance under conditions of varying ambient humidity.

[0010] Another aspect of the present disclosure is to provide a method for controlling the opening and closing of intake and exhaust valves of an internal combustion engine to optimize performance under conditions of varying ambient humidity.

[0011] Yet another aspect of the present disclosure is to provide a method for adjusting the opening and closing of intake and exhaust valves with respect to the position of a crankshaft of an internal combustion engine to optimize performance under conditions of varying ambient humidity.

[0012] Yet another aspect of the present disclosure is to provide a method for adjusting the overlap between the opening of an intake valve and the closing of an exhaust valve of an internal combustion engine to optimize performance under conditions of varying ambient humidity.

[0013] Another aspect of the present disclosure is to provide a method for using lookup tables to adjust the opening and closing of intake and exhaust valves relative to the position of a crankshaft of an internal combustion engine to optimize performance under conditions of varying ambient humidity.

[0014] Yet another aspect of the present disclosure is to provide a method for using lookup tables to adjust the phase of intake and exhaust camshafts relative to the position of a crankshaft to control the opening and closing of intake and exhaust valves of an internal combustion engine to optimize performance under changing ambient humidity.

[0015] Further objects, advantages, and areas of application will become apparent from the description presented herein. It should be noted that the description and specific examples are for illustrative purposes only. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are for illustrative purposes only. Fig. 1 is a functional block diagram of an exemplary internal combustion engine system according to the present disclosure; Fig. 2 is a functional block diagram of an exemplary engine control module (EMC) according to the present disclosure; Fig. 3 is a functional block diagram of an exemplary air control device of an internal combustion engine according to the present disclosure; Fig. 4A, 4B, 4C, and 4D are pictorial representations of three-dimensional lookup tables used to provide minimum and maximum intake and exhaust camshaft phase constraints in accordance with the present disclosure; Fig. 5 is a time-based graphical representation illustrating the operation of intake and exhaust camshaft phasing according to the present disclosure; and Fig. 6 is a flowchart illustrating the steps of the method for controlling the phase of intake and exhaust camshaft phasing according to the present disclosure. DETAILED DESCRIPTION

[0017] The following description is merely exemplary in nature.

[0018] With reference now to Fig. 1 shows a functional block diagram of an exemplary internal combustion engine system 100. The engine system 100 includes a spark-ignition internal combustion engine 102 that combusts a fuel-air mixture to produce drive torque for a vehicle (not shown) based on driver inputs from a driver input module 104.

[0019] The internal combustion engine includes an intake manifold 110 into which air is drawn through throttle valve 112. Throttle valve 112 typically includes a movable throttle plate 113. An engine control module (ECM) 114, discussed in more detail below, controls a throttle actuator module 116, which in turn regulates the opening of throttle plate 113 within throttle valve 112 to control the amount of air drawn into intake manifold 110.

[0020] Air from the intake manifold 110 is drawn into a plurality of cylinders 118 of the engine 102, one of which is Fig. 1. For example, the engine 102 may include 3, 4, 5, 6, 8, 10, or 12 cylinders. The ECM 114 may command a cylinder actuator module 120 to selectively deactivate certain cylinders, which may improve fuel efficiency under certain engine operating conditions.

[0021] Engine 102 operates using a four-stroke cycle. The four strokes are referred to as the intake stroke, compression stroke, combustion stroke, and exhaust stroke. During each revolution of a crankshaft (not shown), two of the four strokes occur within cylinder 118. Therefore, two crankshaft revolutions are necessary for cylinder 118 to complete a full four-stroke combustion cycle.

[0022] During the intake stroke, air is drawn from intake manifold 110 through intake valve 122 into cylinder 118. The ECM 114 controls a fuel actuator module 124, which regulates fuel injection to achieve a specific desired air / fuel ratio. Fuel may be injected into intake manifold 110 at a central location or multiple locations, such as near the intake valve 122 of each cylinder. Alternatively, fuel may be injected directly into the cylinders or into the mixing chambers associated with the cylinders. The fuel actuator module 124 stops injecting fuel into the deactivated cylinders.

[0023] The injected fuel mixes with air to form a fuel / air mixture within cylinder 118. During the compression stroke, a piston 125 within cylinder 118 compresses the air / fuel mixture. Based on a signal from the ECM 114, a spark actuator module 126 applies voltage to a spark plug 128 within cylinder 118, which ignites the fuel / air mixture.

[0024] The ignition actuator module 126 is controlled by a timing signal that determines how long before or after the top dead center (TDC) position of the piston 125 the spark should be generated. Because the piston position is directly related to crankshaft rotation, the operation of the ignition actuator module 126 is preferably synchronized with the crankshaft angle. The ignition actuator module 126 has the capability of constantly varying the timing signal for the ignition spark relative to the top dead center of the piston 125. The spark actuator module 126 can disable ignition for deactivated cylinders.

[0025] During the combustion stroke, the combustion of the fuel / air mixture drives piston 125 away from TDC, thereby driving the crankshaft. The combustion stroke can be defined as the time between the moment piston 125 reaches TDC and the moment the piston reaches bottom dead center (BDC). During the exhaust stroke, piston 125 moves away from BDC and expels the combustion products through an exhaust valve 130. The combustion products are expelled from the vehicle via an exhaust system 134.

[0026] The intake valve 122 is controlled by an intake camshaft 140, while the exhaust valve 130 is controlled by an exhaust camshaft 142. It is understood that the intake camshaft 140 or multiple intake camshafts 140 typically control a plurality of intake valves 122 associated with one or more cylinders 118 in one or more cylinder banks. Likewise, it is understood that the exhaust camshaft 142 or multiple exhaust camshafts 142 typically control a plurality of exhaust valves 130 associated with one or more cylinders 118 in one or more cylinder banks. It is also understood that the intake valve 122 and / or the exhaust valve 130 are controlled by devices other than camshafts, such as camless valve actuators.The cylinder actuator module 120 may deactivate the cylinder 118 by disabling the opening of the intake valve 122 and / or the exhaust valve 130.

[0027] The timing at which intake valve 122 opens and closes relative to piston TDC is varied by an intake cam phaser 148. Similarly, the timing at which exhaust valve 130 opens and closes relative to piston TDC is varied by an exhaust cam phaser 150. A phase actuator module 158 controls intake cam phaser 148 and exhaust cam phaser 150 based on signals from ECM 114. Optionally, variable valve lift may also be controlled by phaser actuator module 158.

[0028] The engine system 100 may include a turbocharger, which in turn includes a turbine 160A driven by the hot exhaust gases flowing through the exhaust system 134. The turbocharger also includes an air compressor 160B driven by the turbine 160A. The compressor 160B compresses the air fed into the throttle valve 112. The turbine 160A and the compressor 160B are coupled by a rotating member, such as a shaft 160C. Although shown separately for clarity, the turbine 160A and the compressor 160B may be adjacent to and secured to each other. Alternatively, a supercharger (not shown) driven by the engine crankshaft compresses air from the throttle valve 112 and delivers it to the intake manifold 110.

[0029] A wastegate 162, arranged in parallel with the turbocharger turbine 160A, allows exhaust gas to bypass the turbine 160A, thereby reducing boost pressure, i.e., the amount of intake air compression provided by the turbocharger. A wastegate actuator module 164 regulates the turbocharger boost pressure by controlling the opening of the wastegate 162. It is understood that two or more turbochargers and wastegates 162 may be used and controlled by the wastegate actuator module 164.

[0030] Optionally, an air cooler (not shown) can be arranged upstream of the intake manifold 110 to transfer heat from the compressed charge air to a cooling medium, such as engine coolant or ambient air. Alternatively, the compressed charge air can be heated, for example, by compression or by components of the exhaust system 134.

[0031] The engine system 100 includes an exhaust gas recirculation (EGR) valve 170 that selectively recirculates exhaust gas to the intake manifold 110. The EGR valve 170 may be located upstream of the turbocharger turbine 160A. The EGR valve 170 is controlled by an EGR actuator module 172 based on signals from the ECM 114.

[0032] The position of the crankshaft is measured using a crankshaft position sensor 180. The speed of the crankshaft, which corresponds to the speed of the engine 102, can be determined based on the crankshaft position. The temperature of the engine coolant is measured by an engine coolant temperature (ECT) sensor 182. The ECT sensor 182 is preferably located within the engine 102 or at another location where the coolant is circulated, such as a radiator (not shown).

[0033] The pressure in the intake manifold 110 may be measured with an intake manifold pressure (MAP) sensor 184. Optionally, the engine vacuum, consisting of the difference between the ambient air pressure and the pressure within the intake manifold 110, may be measured. The mass flow rate of air flowing into the intake manifold 110 is measured with a mass air flow (MAF) sensor 186.

[0034] The throttle actuator module 116 monitors the real-time position of the throttle valve 112 using one or more throttle position sensors (TPS) 190. The temperature of the ambient air drawn into the engine 102 is measured by an intake air temperature (IAT) sensor 192. The humidity of the ambient air drawn into the engine 102 is measured by an intake air humidity (IAT) sensor 193. The engine system 100 may also include additional sensors 194, such as one or more knock sensors, a compressor outlet pressure sensor, a throttle inlet pressure sensor, a wastegate position sensor, an EGR position sensor, and other suitable sensors. The ECM 114 may use signals (outputs) from such sensors to make control decisions for the engine system 100.

[0035] The ECM 114 communicates with a transmission control module 195 to coordinate gear shifting within a transmission (not shown). For example, the ECM 114 may reduce engine torque during a gear shift. The ECM 114 communicates with a hybrid control module 196 to coordinate operation of the engine 102 with an electric motor 198. The electric motor 198 typically also operates as a generator and may be used to generate electrical energy for use in the vehicle's electrical system or for storage in a battery.

[0036] Any system that affects an engine parameter is referred to as an engine actuator. For example, the throttle actuator module 116 adjusts the opening of the throttle valve 112 to achieve a desired throttle opening range. The ignition actuator module 126 controls the ignition timing to achieve a desired spark timing relative to piston TDC. The fuel actuator module 124 controls the injectors to achieve certain fuel delivery setpoints. The phaser actuator module 158 controls the intake and exhaust cam phasers 148 and 150 to achieve desired phase angles for the intake and exhaust cams, respectively. The EGR actuator module 172 controls the EGR valve 170 to achieve a desired EGR opening range. The boost actuator module 164 controls the wastegate 162 to achieve a desired wastegate opening range.The cylinder actuator module 120 controls cylinder deactivation to achieve a desired number of activated and deactivated cylinders.

[0037] The ECM 114 generates the desired engine actuator values ​​to enable the engine 102 to produce a desired engine output torque. The ECM 114 generates the desired engine actuator values ​​using model predictive control, as discussed in more detail below.

[0038] With reference now to Fig. Figure 2 shows a functional block diagram of the engine control module (ECM) 114. The ECM 114 includes a driver torque module 202, a torque request module 224, and an air control module 228.

[0039] The driver torque module 202 determines a requested driver torque 254 based on a driver input 255 from the Fig. 1. Follower input 255 is based, for example, on the position of an accelerator pedal and the position of a brake pedal. Follower input 255 may also be based on a cruise control setting or an adaptive cruise control system that varies vehicle speed to maintain a predetermined following distance.

[0040] The torque request module 224 determines an air torque request 265 based on the drive torque request 254. The air torque request 265 may be a braking torque.

[0041] Engine actuator airflow control targets are determined based on the air torque request 265. More specifically, the air control module 228 determines a wastegate opening range 266, a throttle opening range 267, an EGR opening range 268, a intake cam phaser angle 269, and a exhaust cam phaser angle 270 based on the air torque request 265.

[0042] The boost actuator module 164 controls the wastegate 162 to achieve the wastegate opening range 266. For example, a first conversion module 272 converts the wastegate opening range 266 into a desired duty cycle 274 applied to the wastegate 162, and the wastegate actuator module 164 outputs a signal to the wastegate 162 based on the desired duty cycle 274. Alternatively, the first conversion module 272 converts the wastegate opening range 266 into a desired wastegate position and converts the desired wastegate position to the desired duty cycle 274.

[0043] The throttle actuator module 116 controls the throttle valve 112 to achieve the desired throttle opening area 267. For example, a second conversion module 276 converts the desired throttle opening area 267 into a desired duty cycle 278 applied to the throttle valve 112, and the throttle actuator module 116 outputs a signal to the throttle valve 112 based on the desired duty cycle 278. Alternatively, the second conversion module 276 converts the desired throttle opening area 267 into a desired throttle position and converts the desired throttle position into the desired duty cycle 278.

[0044] The EGR actuator module 172 controls the EGR valve 170 to achieve the desired EGR opening area 268. For example, a third conversion module 280 converts the desired EGR opening area 268 into a desired duty cycle 282 applied to the EGR valve 170, and the EGR actuator module 172 outputs a signal to the EGR valve 170 based on the desired duty cycle 282. Alternatively, the third conversion module 280 converts the desired EGR opening area 268 into a desired EGR position and converts the desired EGR position into the desired duty cycle 282.

[0045] The phaser actuator module 158 controls both the intake cam phaser 148 to adjust the desired intake cam phase angle 269 and the exhaust cam phaser 150 to achieve the desired exhaust cam phase angle 270. Alternatively, a fourth conversion module (not shown) may be included to convert the desired intake cam and exhaust cam phase angles into desired intake and exhaust duty cycles applied to the intake and exhaust cam phasers 148 and 150, respectively. The air control module 228 may also determine a desired overlap factor and a desired effective displacement, and the phaser actuator module 158 may control the intake and exhaust cam phasers 148 and 150 to achieve the desired overlap factor and the desired effective displacement.

[0046] With reference to Fig. 2 and Fig. 3, the air control module 228 includes a torque conversion module 304 that receives the air torque request 265, which, as discussed above, may be a braking torque. A torque conversion module 304 converts the air torque request 265 into base torque. Base torques are referred to as the torque generated at the crankshaft during engine operation 102 using a torque meter while the engine 102 is at operating temperature and the engine 102 is not under torque loads from accessories such as an alternator or an air conditioning compressor. The torque conversion module 304 converts the air torque request 265 into a base air torque request 308, for example, using mapping or a function that maps braking torques to base torques. The torque request resulting from the conversion to base torque is referred to herein as the base air torque request 308.

[0047] A model predictive control (MPC) module 312 generates five target values ​​266 through 270 using a model predictive control scheme. The five target values ​​are: wastegate target value 266, throttle target value 267, EGR target value 268, intake cam phaser angle target value 269, and exhaust cam phaser angle target value 270. A sequence determination module 316 determines possible sequences of the target values ​​266 through 270 to be used together during the future N control loops.

[0048] A prediction module 323 determines predicted responses of the engine 102 to the possible sequences of setpoints 266 to 270 based on a mathematical model 324 of the engine 102, auxiliary inputs 328, and feedback inputs 330. In particular, based on a possible sequence of setpoints 266 to 270, the auxiliary inputs 328, and the feedback inputs 330 using the model 324, the prediction module 323 generates a sequence of predicted torque of the engine 102 for N control loops, a sequence of predicted air-per-cylinder 118 (APCs) for N control loops, a sequence of predicted amounts of external dilution for N control loops, a sequence of predicted amounts of residual dilution for N control loops, a sequence of predicted combustion phaser values ​​for N control loops, and a sequence of predicted combustion quality values ​​for N control loops.

[0049] For example, the model 324 may be a function or a mapping based on characteristics of the engine 102. In this context, dilution refers to an amount of exhaust gas from a previous combustion that remains in a cylinder during combustion. External dilution refers to exhaust gas introduced for combustion via the EGR valve 170. Residual dilution (also referred to as internal dilution) refers to exhaust gas remaining in a cylinder or exhaust gas forced back into the cylinder after the exhaust stroke of a combustion stroke.

[0050] Combustion phasing refers to a crankshaft position at which a predetermined amount of injected fuel combusts in a cylinder relative to a predetermined crankshaft position for combustion of the predetermined amount of injected fuel. For example, combustion phasing can be expressed as CA50 relative to a predetermined CA50. CA50 refers to a crankshaft angle (CA) at which 50 percent of a mass of injected fuel in a cylinder has been combusted. The predetermined CA50 corresponds to a CA50 at which a maximum amount of work is performed by the injected fuel and, in various implementations, is approximately 8.5 to approximately 10 degrees after TDC (top dead center). While combustion phasing is discussed using CA50 values, any other suitable parameter meaningful to combustion phasing may be used.In addition, another suitable parameter that is meaningful for combustion quality can be applied while discussing combustion quality as the coefficient of variation (COV) of the indicated mean effective pressure (IMEP).

[0051] The auxiliary inputs 328 provide parameters that are not directly influenced by the throttle valve 112, the EGR valve 170, the turbocharger, the intake cam phaser 148, and the exhaust cam phaser 150. The auxiliary inputs 328 may include engine speed, turbocharger inlet air pressure, the IAT, or one or more other parameters. The feedback inputs 330 include, for example, an estimated output torque of the engine 102, an exhaust pressure downstream of the turbocharger turbine 160A, the IAT, an APC of the engine 102, an estimated residual dilution, an estimated external dilution, and other suitable parameters. The feedback inputs 330 are measured using sensors (e.g., the IAT 192) or estimated based on one or more other parameters.

[0052] Each of the sequences designated by the sequence determination module 316 includes a sequence of N values ​​for each of the desired values ​​266 through 270. In other words, each possible sequence includes a sequence of N values ​​for the desired wastegate opening range 266, a sequence of N values ​​for the desired throttle opening range 267, a sequence of N values ​​for the desired EGR opening range 268, a sequence of N values ​​for the desired intake cam phaser angle 269, and a sequence of N values ​​for the desired exhaust cam phaser angle 270. Each of the N values ​​represents a corresponding value of the future N control loops. N is an integer greater than or equal to one.

[0053] A cost module 332 determines a cost value for each of the possible sequences of target values ​​266 through 270 based on the predicted parameters determined for a possible sequence and output reference values ​​356. An example cost determination is discussed further below.

[0054] A selection module 344 selects one of the possible sequences of setpoints 266 through 270 based on the respective costs of the possible sequences. For example, the selection module 344 may select the possible sequence with the lowest cost that simultaneously satisfies the actuator constraints 348 and the output constraints 352.

[0055] Satisfaction of actuator constraints 348 and output constraints may be considered in determining costs. In other words, cost module 332 may further determine cost values ​​based on actuator constraints 348 and output constraints 352. As discussed in more detail below, depending on how the cost values ​​are determined, selection module 344 will select the one of the possible sequences that best satisfies base air torque request 208 while minimizing APC, subject to actuator constraints 348 and output constraints 352.

[0056] The selection module 344 sets the target values ​​266 to 270 to the first N values ​​of the selected possible sequence. In other words, the selection module 344 sets the wastegate opening range 266 to the first of the N values ​​in the sequence of N values ​​for the wastegate opening range 266, the desired throttle opening range 267 to the first of the N values ​​in the sequence of N values ​​for the desired throttle opening range 267, the desired EGR opening range 268 to the first of the N values ​​in the sequence of N values ​​for the desired EGR opening range 268, the desired intake cam phaser angle 269 to the first of the N values ​​in the sequence of N values ​​for the desired intake cam phaser angle 269, and the desired exhaust cam phaser angle 270 to the first of the N values ​​in the sequence of N values ​​for the desired exhaust cam phaser angle 270.

[0057] In a next control loop, the MPC module 312 identifies possible sequences, generates the predicted parameters for the possible sequences, determines the costs for each of the possible sequences, selects one of the possible sequences, and sets the setpoints 266 through 270 to the first set of setpoints 266 through 270 in the selected possible sequence. This process continues for each control loop.

[0058] An actuator constraint module 360 ​​sets the actuator constraints 348 for each setpoint 266 through 270. That is, the actuator constraint module 360 ​​sets actuator constraints for the throttle valve 112, actuator constraints for the EGR valve 170, actuator constraints for the wastegate valve 162, actuator constraints for the intake cam phaser 148, and actuator constraints for the exhaust cam phaser 150.

[0059] With reference to Fig. 2, Fig. 3 and Fig. 4A, Fig. 4B, Fig. 4C and Fig. 4D, the actuator constraint module 360 ​​sets the actuator limits or constraints for a given actuator to follow a predetermined schedule that depends on operating conditions of the engine 102, such as speed, load, and ambient conditions. In particular, the actuator constraint module 360 ​​sets the actuator constraints for the intake cam phaser 148 and the exhaust cam phaser 150 to follow a predetermined schedule that depends on engine speed, load, and ambient humidity in order to limit the amount of dilution in the combustion system or to maintain the combustion quality, and thus the performance, of the engine 102 at an acceptable level. Accordingly, the actuator constraint module 360 ​​receives the signal or output of the ambient humidity sensor 193 and uses it in conjunction with the three-dimensional lookup tables included in the Fig. 4A, Fig. 4B, Fig. 4C and Fig. 4D to generate minimum and maximum actuator constraints for both the intake cam phaser 148 and the exhaust cam phaser 150. Alternatively, the ambient humidity may be estimated based on, for example, current and past ambient conditions and operating parameters.

[0060] The Fig. The three-dimensional lookup table 372 illustrated in Figure 4A is used to generate a minimum setpoint for the intake cam phaser 148. It uses revolutions per minute of the engine 102 on the horizontal (X) axis, engine load on the vertical (Y) axis, and ambient humidity on a diagonal (Z) axis. It is understood that the Z axis is functionally perpendicular to the plane of the X and Y axes, but in Fig. 4A, as well as 4B, 4C, and 4D is shown diagonally due to the two-dimensional limitations of the drawings. The XY plane 373A represents a dry, minimum humidity, and the XY plane 373B represents a wet, minimum humidity. The lookup table 372 contains experimental and empirical values ​​that provide a specific, predetermined minimum value or target constraint 374 for the intake cam phaser 148 based on the current values ​​of the three variables. Similarly, the Fig. 4B illustrates lookup table 376. RPM of engine 102 on the horizontal (X) axis, engine load on the vertical (Y) axis, and ambient humidity on a diagonal (Z) axis. XY plane 377A represents a dry maximum humidity, and XY plane 377B represents a wet maximum humidity. Lookup table 376 contains experimental and empirical values ​​that provide a specific, predetermined maximum value or target constraint 378 for intake cam phaser 148 based on the current values ​​of the three variables.

[0061] The Fig. The three-dimensional lookup table 380 illustrated in Figure 4C uses revolutions per minute of the engine 102 on the horizontal (X) axis, engine load on the vertical (Y) axis, and ambient humidity on a diagonal (Z) axis. The XY plane 381A represents a dry, minimum humidity, and the XY plane 381B represents a wet, minimum humidity. The lookup table 380 contains experimental and empirical values ​​that provide a specific, predetermined minimum value or target constraint 382 for the exhaust cam phaser 150 based on the current values ​​of the three variables. Similarly, the Fig. 4D illustrates three-dimensional lookup table 384. RPM of engine 102 on the horizontal (X) axis, engine load on the vertical (Y) axis, and ambient humidity on a diagonal (Z) axis. XY plane 385A represents a dry maximum humidity, and XY plane 385B represents a wet maximum humidity. Lookup table 384 contains experimental and empirical values ​​that provide a specific, predetermined maximum value or target constraint 386 for exhaust cam phaser 150 based on the current values ​​of the three variables.

[0062] With brief reference to Fig. 5, the dynamic operation of the intake cam phaser 148 and the exhaust cam phaser 150 is illustrated in a graph 390, with ambient humidity varying over time along the horizontal (X) axis. In the lower portion of the graph 390 are four traces representing the intake cam phase value or intake cam phase position (ICPV). The lowest line or trace 391 is flat and represents the maximum ICPV retard constraint generated or commanded by the actuator constraint module 360. On the right side of the graph 390, the next highest line or trace 392 represents a reference ICPV constraint provided to the intake cam phaser 148 by the actuator constraint module 360 ​​without compensation for humidity.On the right side of the graph 390, the third line or trace 393 represents the maximum ICPV cam advance limitation provided to the intake cam phaser 148 by the high humidity actuator limitation module 360. The top line 394 in the graph 390 represents the maximum ICPV cam advance limitation provided to the intake cam phaser 148 by the low humidity actuator limitation module 360.

[0063] The upper portion of the graph 390 shows similar information regarding the exhaust cam phase value or camshaft phase position (ECPV). The top line or trace 395 is flat and represents the maximum ECPV advance constraint generated or commanded by the actuator constraint module 360. On the right side of the graph 390, the next lower line or trace 396 represents an ECPV reference constraint provided to the exhaust cam phaser 150 by the actuator constraint module 360 ​​without compensation for humidity. On the right side of the graph 390, the third line or trace 397 represents the maximum ECPV cam retard constraint provided to the exhaust cam phaser 150 by the actuator constraint module 360 ​​with high humidity.Finally, line 398 in graph 390 represents the maximum ECPV cam retardation constraint provided to the exhaust cam phaser 150 by the actuator constraint module 360 ​​at low humidity. It can be seen from lines or traces 391 through 398 of graph 390 that, with increasing humidity, optimal operation of the engine 102 requires less overlap between the closing of the exhaust valve(s) 130 and the opening of the intake valve(s) 122, and vice versa.

[0064] With further reference to Fig. 2 and Fig. 3, the actuator constraints 348 for the other setpoints 266, 267, and 268 may also include a maximum and minimum value for an associated target. Furthermore, the actuator constraint module 360 ​​may adjust one or more actuator constraints 348 under certain circumstances. For example, if a fault is diagnosed in that actuator circuit, the actuator constraint module 360 ​​may adjust the actuator constraints to narrow the operating range for that actuator.

[0065] An output constraint module 364 sets the output constraints 352 for the predicted torque output of the engine 102, the predicted CA50, the predicted COV of the IMEP, the predicted residual dilution, and the predicted external dilution. The output constraints 352 for each predicted value may include a maximum value for an associated predicted parameter and a minimum value for that predicted parameter. For example, the output constraints 352 may include a minimum torque, a maximum torque, a minimum CA50 and a maximum CA50, a minimum IMEP COV and a maximum IMEP COV, a minimum residual dilution and a maximum residual dilution, and a minimum external dilution and a maximum external dilution.

[0066] The output constraint module 364 generally sets the output constraints 352 to predetermined ranges for the associated predicted parameters. However, the output constraint module 364 may vary one or more output constraints 352 under certain conditions. For example, the output constraint module 364 may delay the maximum CA50 when knocking phenomena occur in the engine 102.

[0067] A reference module 368 generates the reference values ​​356 for setting each of the setpoints 266 through 270. Thus, the reference values ​​356 include a reference for the wastegate opening range, a reference for the throttle opening range, a reference for the EGR valve opening range, a reference for the intake cam phaser angle 269, and a reference for the exhaust cam phaser angle 270.

[0068] The reference module 368 determines the reference values ​​356 based, for example, on the air torque request 265, the base air torque request 308, and / or one or more suitable parameters. The reference values ​​356 can be used to determine the cost values ​​for possible sequences.

[0069] The MPC module 312 determines the setpoints 266 through 270 using a quadratic program (QP) solver, such as the Dantzig QP solver. For example, the MPC module 312 may generate a surface of cost values ​​for the possible sequences of setpoints 266 through 270 and, based on the slope of the cost surface, identify a set of possible setpoints with the lowest cost. The MPC module 312 then examines this set of possible setpoints to determine if the set of possible setpoints will satisfy the actuator constraints 348 and the output constraints 352. The MPC module 312 selects the set of possible setpoints with the lowest cost values ​​while satisfying the actuator constraints 348 and the output constraints 352.

[0070] The cost module 332 determines the costs for the possible sequences of setpoints 266 through 270 based on relationships between: the predicted torque and the base air torque request 308; the predicted APC and zero; the possible setpoints and the respective actuator constraints 348; the other predicted parameters and the respective output constraints 352; and the possible setpoints and the respective reference values ​​356.

[0071] In operation, the MPC module 312 determines the cost values ​​for the candidate sequences. The MPC module 312 then selects one of the candidate sequences with the lowest cost. The MPC module 312 also determines whether the selected candidate sequence satisfies the actuator constraints 348. If so, the candidate sequence is used. If not, the MPC module 312 determines a candidate sequence that satisfies the actuator constraints 348 and has the lowest cost based on the selected candidate sequence.

[0072] Referring to Fig.6, a flowchart illustrating the steps of the method for controlling the phase of the intake and exhaust camshaft phasers 148 and 150, respectively, is shown and is generally designated by the number 400. The method 400 begins with a start-up or initialization step 402, which clears registers if necessary and begins a repetition of the steps of the method 400. Next, a method step 404 reads the signal from the intake air humidity sensor 192 or estimates the relative humidity. The method 400 then proceeds to a method step 406 in which the current speed of the engine 102 is read and the torque load of the engine 102 is determined, for example, from data from the torque request module 224. Next, the reference module 368 performs a method step 408, which determines the intake cam phase reference value and the exhaust cam reference value.

[0073] The actuator constraint module 360 ​​performs a subsequent method step 410, which uses the lookup tables 372, 376, 380, and 384 to determine the minimum and maximum constraints of the intake and exhaust cam phasers 148 and 150 for the current values ​​of engine speed, load, and humidity. A decision point 410 then queries whether the reference values ​​determined in step 408 are greater than the constraints determined in step 410. If the reference values ​​are not greater than the constraints, the decision point 412 is exited at NO, and the method 400 ends at an end point 414. If the reference values ​​are greater than the constraints, the decision point 412 is exited at YES, and a method step 416 limits the reference values ​​to the constraints determined in step 410. The method 400 then ends at the end point 414.In general, these minimum and maximum constraints allow less overlap of the inlet and exhaust phasing at higher humidity and more overlap at lower humidity.

[0074] As used herein, the term module includes, but is not limited to, an application-specific integrated circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit or integrated circuit; a combinational logic circuit; a field-programmable gate array; a processor or microprocessor that executes code; memory that stores code executed by a processor; or other suitable hardware components that provide the described functionality.

Claims

[1] A method for controlling the intake and exhaust cam phaser (148, 150) in an internal combustion engine (102) to adjust the valve overlap, comprising the following steps: sensing an engine speed and engine load of the internal combustion engine (102), Detecting the coolant temperature in the internal combustion engine (102), sensing the relative humidity of the air supplied to the combustion engine (102), using the engine speed, engine load, and humidity in a lookup table to determine the minimum and maximum intake cam phase limit values ​​and the minimum and maximum exhaust cam phase limit values, and advancing the maximum exhaust cam phasing and retarding the maximum intake cam phasing based on coolant temperature as relative humidity increases, thereby reducing valve overlap. [2] The method of claim 1, wherein the lookup table is three-dimensional. [3] The method of claim 1, wherein the engine load is based on a torque request to an air control module. [4] The method of claim 1, wherein the intake cam phaser (148) is coupled to and moves an intake camshaft (140) and the exhaust cam phaser (150) is coupled to and moves an exhaust camshaft (142).

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