Coordination of secondary air and blow-through air supply

Abstract

Procedure comprising: Supplying compressed air through a throttle valve to an engine from a compressor driven by a turbine coupled to an exhaust of the engine; and while depressing an accelerator pedal to adjust the throttle valve, reducing turbo lag by supplying ambient air to the turbine during a first operating mode and, during a second operating mode, providing blow-through of a portion of the compressed air through the engine to the turbine without combustion, further comprising a third operating mode which simultaneously comprises supplying ambient air to the turbine and providing blow-through of a portion of the compressed air through the engine to the turbine without combustion, wherein the first operating mode occurs when a pressure difference between the air pressure downstream of the throttle valve and the pressure of the exhaust gas is less than a first threshold, and wherein the second operating mode occurs when a pressure difference between the air pressure downstream of the throttle valve and the pressure of the exhaust gas exceeds a second threshold.

Description

Technical area

[0001] The present description generally relates to methods and systems for improving turbo lag and torque output with the coordination of secondary air injection and blow-by air in a turbocharged internal combustion engine. Background and Summary

[0002] A turbocharged engine can offer greater fuel efficiency and lower emissions than a naturally aspirated engine of similar power. However, during transient conditions, the power, fuel efficiency, and emissions control performance of a turbocharged engine can suffer. Such transient conditions can include rapidly increasing or decreasing engine load, engine speed, or mass airflow. For example, when engine load increases rapidly, a turbocharged compressor may require increased torque to deliver increased airflow. Such torque may not be available if the turbine driving the compressor is not fully spun up. Consequently, an undesirable power lag can occur before intake airflow builds to the required level.

[0003] It was previously recognized that a turbocharged engine system can be designed to provide "blow-by" air, whereby boosted intake air is forced from the intake manifold downstream of the compressor, through the engine cylinder(s) and into the exhaust manifold upstream of the turbine. A variable cam timing (VCT) system, for example, can be temporarily set to create high valve overlap. During positive valve overlap, the boosted air is forced through the cylinders into the turbine to temporarily create additional mass flow and enthalpy in the exhaust. The additional turbine energy allows the turbine to spin up faster, reducing turbo lag.

[0004] DE 10 2004 009 290 A1 is known from the prior art. This describes a method for controlling an internal combustion engine with an exhaust gas turbocharger, a throttle valve, and a secondary air pump.

[0005] EP 1 591 651 A1 describes a method for increasing torque in the lower speed range of a supercharged internal combustion engine by means of additional combustion air that is supplied separately.

[0006] However, the inventors have recognized potential problems with such an approach. For example, to achieve blowby, the engine must be in positive surge (i.e., under boosted engine operation), otherwise turbocharger performance may be degraded. During blowby, the engine may also be operated at high levels of spark retard to deliver additional energy to the exhaust gas to increase turbine speed and boost. However, operating the engine at high levels of spark retard may cause combustion to occur later than the optimal timing required for immediate torque output.

[0007] Methods having the features of claims 1, 8 and 12 are provided.

[0008] Accordingly, at least some of the above problems may be addressed by a method for a turbocharged engine comprising: supplying compressed air through a throttle to an engine from a compressor driven by a turbine coupled to an exhaust of the engine; and during depressing an accelerator pedal to adjust the throttle, reducing turbo lag by supplying ambient air to the turbine during a first mode of operation, and during a second mode of operation, providing blow-by of a portion of the compressed air through the engine without combustion to the turbine.

[0009] For example, in response to accelerator pedal depressing, a secondary air pump may be used to supply secondary air into an exhaust manifold upstream of a turbine. Concurrently, enrichment may be provided to generate high levels of carbon monoxide (CO), hydrogen (H2), and hydrocarbons from the engine to react with the secondary air in the exhaust. Consequently, the mass and enthalpy of the exhaust gas may be increased, which may be used to increase turbine speed to a desired speed. Further, due to the increase in turbine speed, boost pressure may be increased. Upon reaching a threshold boost pressure at which sufficient boost may be available for blowby, engine operation may switch to providing blowby. That is, secondary air introduction may be stopped, and blowby may be used to provide additional air in the exhaust.

[0010] In some examples, upon reaching the threshold boost pressure, a secondary air injection amount may be decreased and simultaneously the blowby air amount may be increased until the secondary air injection amount decreases below a threshold amount, after which the engine may be operated with only blowby until the desired turbine speed is reached.

[0011] By providing secondary air injection early during accelerator pedal depressurization, sufficient boost can be generated to be used for blow-by. Consequently, turbocharger performance can be improved. Using secondary air injection during the initial portion of accelerator pedal depressurization can also allow for higher trapped mass in the cylinder (since the additional air in the exhaust required for additional exhaust energy is supplied by the secondary air pump rather than the turbocharger). Consequently, initial torque output can be improved. In addition, using secondary air injection during the early portion of accelerator pedal depressurization, valve timing can be adjusted to increase initial torque output.Furthermore, by switching engine operation to provide additional or alternative blow-by after sufficient boost is achieved, the time required for the turbine to reach a desired speed can be shortened, thereby reducing turbo lag. In this way, secondary air injection and blow-by can be coordinated during accelerator pedal depressing to accelerate turbine spin-up and improve initial torque output.

[0012] Of course, the above summary is provided to introduce, in a simplified form, a selection of concepts 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 only by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages identified above or in any part of this disclosure. Brief description of the drawings Fig. 1 shows a schematic representation of a power machine system. Fig. Figure 2 shows a schematic diagram of a cylinder of the engine system of Fig. 1. Fig. Figure 3 shows a high-level flowchart illustrating a routine that can be implemented to coordinate secondary air injection and blow-by during an accelerator pedal depression to reduce turbo lag. Fig. Figure 4 shows a high-level flow chart illustrating a routine that can be implemented to provide secondary air injection, which in conjunction with Fig. 3 should be used. Fig. Figure 5 shows a high-level flow chart illustrating a routine that can be implemented to provide blow-through, which in conjunction with Fig. 3 should be used. Fig. Figure 6 shows a high-level flow chart illustrating a routine that can be implemented to increase the blow-by amount while decreasing the secondary air introduction amount used in conjunction with Fig. 3 should be used. Fig. 7 shows example secondary air and blow-by settings to reduce turbo lag, according to the present disclosure. Detailed description

[0013] Methods and systems are provided for reducing turbo lag in a vehicle engine such as the one in Fig. 1-2. During an accelerator pedal depression, secondary air injection and blow-through may be coordinated to accelerate the rotation of a turbine to a desired speed and increase torque output. A control unit may be configured to execute control routines, such as the example routines of Fig. 3-6 to determine a type of engine operation that can be performed while the accelerator pedal is depressed (e.g., secondary air injection and / or blow-by), and adjust the engine operation based on the type of operating mode. The example secondary air injection and blow-by settings are shown at Fig. 7 described.

[0014] Fig. 1 shows a schematic representation of a vehicle system 106. The vehicle system 106 includes an engine system 108 with an engine 100 coupled to an emissions control system 122. The engine 100 includes a plurality of cylinders 14. The engine 100 also includes an intake 123 and an exhaust 125. The intake 123 may receive fresh air from the atmosphere through an intake passage 142. Air entering the intake passage 142 may be filtered by an air filter 191. The intake passage 142 may include an air intake throttle 164 disposed downstream of an intake compressor 152 and an intake charge air cooler 184. The intake throttle 164 may be configured to adjust the flow of intake gas (e.g., boosted intake air) entering the engine intake manifold 146.The exhaust 125 includes an exhaust manifold 148 leading to an exhaust passage 145 that directs exhaust gas to the atmosphere via an exhaust pipe 135.

[0015] The engine 100 may be a boosted engine with a boosting device such as a turbocharger 161. The turbocharger 161 may include an intake compressor 152 disposed along the intake passage 142 and an exhaust turbine 154 disposed along the exhaust passage 145. The compressor 152 may be driven at least partially by the turbine 154 via a shaft 180. The amount of boost provided by the turbocharger may be varied by an engine control unit. A turbine bypass passage 163, controlled by a wastegate 165, may be coupled across the exhaust turbine so that some or all of the exhaust gases flowing through the exhaust passage 145 may bypass the turbine 154.By adjusting the position of the wastegate, an amount of exhaust gas supplied through the turbine can be changed, thereby changing an amount of boost delivered to the engine intake.

[0016] In further embodiments, a similar bypass passage, controlled by a bypass valve (not shown), may be coupled across the intake compressor so that some or all of the intake air compressed by compressor 152 may be recirculated into the intake passage 142 upstream of compressor 152. By adjusting the position of the compressor bypass valve, the pressure in the intake system may be relieved during selected conditions to reduce the effects of compressor surge loading.

[0017] An optional charge air cooler 184 may be included in the intake passage downstream of the compressor 152 to reduce the temperature of the intake air compressed by the turbocharger. In particular, an aftercooler 184 may be included upstream of the intake throttle 164 or integrated into the intake manifold 144.

[0018] The emission control system 122, coupled to the exhaust passage 145, includes an emission control device 178. In one example, the emission control device 178 may include multiple catalyst modules. In another example, multiple emission control devices, each with multiple modules, may be used. The emission control device 178 may, in one example, be a three-way catalyst. In other examples, the emission control device 178 may be an oxidation catalyst, a lean NOx trap, a selective catalyst reduction (SCR) device, a particulate filter, or another exhaust treatment device.Although the emission control device 178 is disposed downstream of the turbine 154 in the embodiments described herein, in other embodiments the emission control device 178 may be disposed upstream of a turbocharger turbine or at another location in the engine exhaust passage without departing from the scope of this disclosure.

[0019] In some examples, the vehicle system 106 may further include a low-pressure exhaust gas recirculation (LP-EGR) system (not shown). The LP-EGR system may include an LP-EGR passage coupling the exhaust passage 145 downstream of the emission control device 178 to an air intake passage 142 upstream of the compressor 152. An EGR cooler (not shown) and an LP-EGR valve (not shown) may be disposed in the LP-EGR passage to cool the exhaust gas flowing therethrough and to vary an amount and / or rate of exhaust gas recirculated from the exhaust passage to the intake passage via the LP-EGR system, respectively.

[0020] In some examples (as shown), the vehicle system 106 may further include a high-pressure EGR (HP EGR) system 171. The HP EGR system 171 includes an EGR passage 173 coupling the exhaust passage 145 upstream of the turbine 154 to the air intake passage 142 downstream of the compressor 152 and upstream of the charge air cooler 184 and the intake throttle 164. An EGR cooler 172, disposed within the EGR passage 173, cools the exhaust gas flowing therethrough. A position of an EGR valve 179 disposed in the EGR passage 173 on the inlet passage side of the EGR cooler 172 may be adjusted by the control unit 120 to adjust an amount and / or a rate of exhaust gas recirculated from the exhaust passage to the inlet passage via the HP EGR system.In some embodiments, one or more sensors may be disposed within the HP-EGR passage 173 to provide an indication of one or more of a pressure, a temperature, and an air / fuel ratio of the exhaust gas recirculated through the HP-EGR passage.

[0021] The engine 100 may be controlled at least in part by a control system 140 including a control unit 120 and by input from a vehicle driver via an input device (not shown). The control system 140 is configured to receive information from a plurality of sensors 160 (various examples of which are described herein) and send control signals to a plurality of actuators 181. As an example, the sensors 160 may include an exhaust oxygen sensor 126 coupled to the exhaust manifold 148, a MAP sensor 121 coupled to the intake manifold 144, an exhaust catalyst temperature sensor 117, an exhaust pressure sensor 119 disposed upstream of the emission control device 178 in the exhaust pipe 135, an exhaust temperature sensor 127, and an exhaust pressure sensor 129 disposed downstream of the emission control device 178 in the exhaust pipe 135.Various exhaust gas sensors may also be included in the exhaust passage 145 downstream of the emission control device 178, such as particulate matter (PM) sensors, NOx sensors, oxygen sensors, ammonia sensors, hydrocarbon sensors, etc. Other sensors, such as additional pressure, temperature, air / fuel ratio, and composition sensors, may be coupled to various locations in the vehicle system 106. As another example, the actuators 181 may include a fuel injector 166, an EGR valve 159, and an intake throttle 164. Other actuators, such as a variety of additional valves and throttle bodies, may be coupled to various locations in the vehicle system 106.The control unit 120 may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on a command or code programmed therein according to one or more routines. Example control routines are described herein with respect to . Fig. 3-6 described.

[0022] As further discussed here with reference to Fig. 3 and Fig. 4, the control unit 120 may be configured to introduce a secondary air flow into the exhaust passage upstream of the turbine to increase exhaust energy during selected engine operating conditions (e.g., during an early portion of an accelerator pedal depression). An air pump 96 may be present to introduce outside air (e.g., from the atmosphere) into the exhaust manifold 148 via an introduction line 94 controlled by a valve 95. As such, the air pump 96 used to reduce turbo lag, as discussed herein, may be designed with a higher flow rate relative to an air pump that may be used for a cold start. In one example, the air pump 96 may introduce outside air into the exhaust passage 135 at a location downstream of the turbine and upstream of the catalyst. As described herein with reference to Fig. 3 and Fig. 5, the controller 120 may be further configured to adjust the VCT system to a timing that provides a high positive valve overlap to deliver blow-by air to the exhaust manifold upstream of the turbine during selected engine operations (e.g., during a later portion of accelerator pedal depression). In some examples, as described herein with reference to Fig. 3 and Fig. 6, the control unit 120 may simultaneously adjust the secondary air introduction and blow-by during selected engine operations (e.g., during an intermediate portion of the accelerator pedal depression between the early portion and the late portion). In this manner, as described herein with reference to Fig. 3-6, the control unit may be configured to coordinate secondary air introduction and VCT blow-by timing to reduce turbo lag and increase initial torque output.

[0023] Fig. 2 illustrates an example embodiment of a combustion chamber or cylinder of internal combustion engine 100. Engine 100 may receive control parameters from a control system including control unit 120 and input from a vehicle driver 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder (herein also "combustion chamber") 14 of engine 100 may include combustion chamber walls 136 with a piston 138 disposed therein. Piston 138 may be coupled to a crankshaft 141 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 141 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system.Furthermore, a starter motor may be coupled to the crankshaft 141 via a flywheel to enable a starting operation of the engine 100.

[0024] Cylinder 14 may receive intake air via a series of intake air passages 142, 144, and 146. Intake air passage 146 may communicate with other cylinders of engine 100 in addition to cylinder 14. In some embodiments, one or more of the intake passages may include a boosting device, such as a turbocharger or a supercharger. Fig. For example, Figure 1 shows engine 100 configured with a turbocharger having a compressor 152 disposed between intake passages 142 and 144 and an exhaust turbine 154 disposed along exhaust passage 145. Compressor 152 may be driven at least partially by exhaust turbine 154 via a shaft 180 when the boosting device is configured as a turbocharger. However, in other examples, such as when engine 100 is provided with a supercharger, exhaust turbine 154 may optionally be omitted, wherein compressor 152 may be driven by a mechanical input from an engine or from the engine. A throttle valve 20 having a throttle plate 164 may be provided along an intake passage of the engine for varying the flow rate and / or pressure of intake air delivered to the engine cylinders.The throttle valve 20 may, for example, be arranged downstream of the compressor 152, as shown here, or may alternatively be provided upstream of the compressor 152.

[0025] The exhaust manifold 148 may receive exhaust gases from other cylinders of the engine 100 in addition to cylinder 14. An exhaust passage 145 may be coupled to the exhaust manifold 148. An exhaust gas sensor 128 is shown coupled to the exhaust passage 148 upstream of the emission control device 178. The sensor 128 may be selected from various suitable sensors for providing an indication of the exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wideband exhaust gas oxygen sensor), a dual-state oxygen sensor or EGO (as shown), a HEGO (heated EGO), a NOx, HC, or CO sensor. The emission control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof.

[0026] The exhaust temperature may be estimated by one or more temperature sensors (not shown) disposed in exhaust passage 145. Alternatively, the exhaust temperature may be inferred based on engine operating conditions such as speed, load, air / fuel ratio (AFR), spark retard, etc. Further, the exhaust temperature may be calculated by one or more exhaust sensors 128. It can be appreciated that the exhaust temperature may alternatively be estimated by any combination of temperature estimation methods listed herein.

[0027] Each cylinder of engine 100 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown with at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in an upper region of cylinder 14. In some embodiments, each cylinder of engine 100, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

[0028] The intake valve 150 may be controlled by the control unit 120 through cam actuation via a cam actuation system 151. Likewise, the exhaust valve 156 may be controlled by the control unit 120 via a cam actuation system 153. The cam actuation systems 151 and 153 may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems, which may be actuated by the control unit 120 to vary valve operation. The position of the intake valve 150 and the exhaust valve 156 may be determined by valve position sensors 155 and 157, respectively. In alternative embodiments, the intake and / or exhaust valves may be controlled by electrical valve actuation.For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation, including CPS and / or VCT systems. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system.

[0029] Cylinder 14 may have a compression ratio that is the ratio of volumes when piston 138 is at bottom dead center to top dead center. Conventionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may occur, for example, when using higher octane fuels or fuels with higher latent heat of vaporization. The compression ratio may also be increased when using direct injection due to its effect on engine knock.

[0030] In some embodiments, each cylinder of engine 100 may include a spark plug 192 for initiating combustion. An ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to an ignition pre-ignition signal SA from controller 120 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 100 may initiate combustion through auto-ignition or by injecting fuel, as may be the case with some diesel engines, for example.

[0031] In some embodiments, each cylinder of engine 100 may be configured with one or more fuel injectors for supplying fuel thereto. As a non-limiting example, cylinder 14 is shown with a fuel injector 166. Fuel injector 166 is shown directly coupled to cylinder 14 for injecting fuel directly therein in proportion to the pulse width of a signal FPW received from control unit 120 via an electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereinafter also referred to as "DI") of fuel into combustion cylinder 14. Although Fig. 1 shows the injector 166 as a side-mounted injector, it may also be located above the piston, such as near the position of the spark plug 192. Such a position may improve mixing and combustion when the engine is running on an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located above and near the intake valve to improve mixing. Fuel may be supplied to the fuel injector 166 from a high-pressure fuel system 8, including fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel may be supplied by a single-stage fuel pump at a lower pressure, in which case the timing of direct fuel injection during the compression stroke may be more limited than when a high-pressure fuel system is used.Although not shown, the fuel tanks may further include a pressure transducer that provides a signal to control unit 120. It will be appreciated that in an alternative embodiment, injector 166 may be a port injector that delivers fuel into the intake port upstream of cylinder 14.

[0032] It will also be appreciated that although the illustrated embodiment illustrates the engine operated by injecting fuel via a single direct injector, in alternative embodiments, the engine may be operated using two injectors (e.g., a direct injector and a port injector) and varying a relative amount of injection from each injector.

[0033] Fuel may be delivered by the injector to the cylinder during a single cycle of the cylinder. Furthermore, the distribution and / or relative amount of fuel delivered by the injector may vary with operating conditions. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any suitable combination thereof. Fuel may also be injected during the cycle to adjust the air-to-injected-fuel ratio (AFR) of the combustion. For example, the fuel may be injected to create a stoichiometric AFR. An AFR sensor may be included to provide an estimate of the AFR in the cylinder. In one example, the AFR sensor may be an exhaust gas sensor such as an exhaust gas temperature sensor (FAT).an EGO sensor 128. By measuring an amount of residual oxygen (for lean mixtures) or unburned hydrocarbons (for rich mixtures) in the exhaust gas, the sensor can determine the AFR. As such, the AFR can be provided as a lambda value (λ value), that is, the ratio of the actual AFR to stoichiometry for a given mixture. Consequently, a lambda of 1.0 indicates a stoichiometric mixture; mixtures richer than stoichiometry may have a lambda value less than 1.0, and mixtures leaner than stoichiometry may have a lambda value greater than 1.

[0034] As described above, Fig. 2 only one cylinder of a multi-cylinder engine. In principle, each cylinder may also include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0035] Fuel tanks in the fuel system 8 may hold fuel with different fuel qualities, such as different fuel compositions. These differences may include different alcohol content, different octane rating, different latent heat of vaporization, different fuel blends, and / or combinations thereof, etc.

[0036] The engine 100 may further include a knock sensor 90 coupled to each cylinder 14 for identifying abnormal cylinder combustion events. In alternative embodiments, one or more knock sensors 90 may be coupled to suitable locations on the engine block. The knock sensor may be an accelerometer on the cylinder block or an ionization sensor configured in the spark plug of each cylinder. The output of the knock sensor may be combined with the output of a crankshaft acceleration sensor to indicate an abnormal combustion event in the cylinder.

[0037] The control unit 120 is shown as a microcomputer having a microprocessor unit 105, input / output ports 107, an electronic storage medium for executable programs and calibration values, shown as a read-only memory chip 110 in this particular example, a random access memory 112, a latch 114, and a data bus.Control unit 120 may receive various signals from sensors coupled to engine 100 in addition to the signals previously discussed, including measurements of inducted mass air flow (MAF) from mass air flow sensor 111; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a profile ignition pickup (PIP) signal from a Hall effect sensor 115 (or other type) coupled to crankshaft 141; throttle position (TP) from a throttle position sensor; a manifold absolute pressure (MAP) signal from sensor 124, cylinder AFR from EGO sensor 128, and abnormal combustion from knock sensor 90 and a crankshaft acceleration sensor. An engine speed signal RPM may be generated by control unit 120 from the PIP signal.The manifold pressure signal MAP from a manifold pressure sensor can be used to provide an indication of the vacuum or pressure in the intake manifold.

[0038] The storage medium read-only memory 110 may be programmed with computer-readable data representing instructions executable by a processor 105 for performing the methods described below, as well as other variations that are expected but not specifically listed. Example routines are described with reference to Fig. 3-6 shown.

[0039] It will be appreciated that, although the present example is described with reference to a turbocharged engine with blow-by capabilities, the setting of engine operating parameters such as fuel richness levels, blow-by thresholds, temperature thresholds, etc., in other embodiments may be calibrated to operate optimally for a particular engine, powertrain, and / or vehicle combination.

[0040] 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 a variation or combination thereof. Furthermore, in some embodiments, other engine configurations may be used, such as a diesel engine.

[0041] During operation, each cylinder within engine 100 typically undergoes a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. During the intake stroke, exhaust valve 156 generally closes and intake valve 150 opens. Air is introduced into combustion chamber 14 via intake manifold 146, and piston 138 moves toward the bottom of the cylinder to increase the volume within combustion chamber 14. The position where piston 138 is near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber 14 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 150 and exhaust valve 156 are closed.Piston 138 moves toward the cylinder head to compress the air within combustion chamber 14. The point at which piston 138 is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber 30 is at its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process referred to below as injection, fuel is introduced into the combustion chamber. In a process referred to below as ignition, fuel is ignited by known ignition means such as spark plug 192, resulting in combustion. During the expansion stroke, the expanding gases push piston 138 back to BDC. Crankshaft 40 translates the piston motion into rotating shaft torque.Finally, during the exhaust stroke, exhaust valve 156 opens to discharge the combusted air / fuel mixture to exhaust manifold 48, and the piston returns to TDC. Note that the above is described merely as an example, and intake and exhaust valve opening and / or closing timing may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0042] Based on the timing differences between exhaust valve closing and intake valve opening, the valves may be operated with negative valve overlap, where both the intake and exhaust valves are closed for a brief duration after the end of the exhaust stroke and before the start of the intake stroke. This period of time during which both valves are closed is referred to as negative (intake-to-exhaust) valve overlap. In one example, the VCT system may be adjusted so that the negative intake-to-exhaust valve overlap timing may be a target engine cam position during cylinder combustion.

[0043] Alternatively, the valves may be operated with positive valve overlap, where both the intake and exhaust valves may be open for a short duration before the end of the exhaust valve lift and after the start of the intake stroke. This period of time during which both valves may be open is referred to as positive (intake to exhaust) valve overlap. The VCT system may be adjusted so that an amount of positive valve overlap increases positive valve overlap during selected operating conditions of a boosted engine. In particular, a position of the intake camshaft may be adjusted to advance intake valve opening timing. Consequently, the intake valve may be opened earlier before the end of the exhaust stroke, and a duration for which both valves are open may be increased, resulting in more positive valve overlap.As one example, positive valve overlap may be increased by moving the intake camshaft from a position of some positive valve overlap to a position with more positive valve overlap. As another example, positive valve overlap may be increased by moving the intake camshaft from a position of negative valve overlap to a position of positive valve overlap. In one example, the VCT system may be adjusted so that the negative intake-to-exhaust valve overlap timing may be a target engine cam position during an engine cold start.

[0044] It can be appreciated that while the above example suggests increasing positive valve overlap by advancing intake opening timing, in alternative examples, positive valve overlap may be increased by adjusting an exhaust camshaft to retard exhaust valve closing. Even further, each of the intake and exhaust camshafts may be adjusted to vary positive valve overlap by altering both intake and exhaust valve timing. In other examples, cam lobe switching or variable valve lift may be used instead of variable camshaft timing.

[0045] In engine system 100, during periods of rapidly increasing engine load, such as immediately after start-up, during accelerator pedal depressing, or upon exiting deceleration fuel shutoff (DFSO), the amount of intake air compression provided by the compressor may be inadequate. During at least some of these conditions, the amount of boost pressure available from the compressor may be limited due to the turbine not being spun up to a sufficiently high speed (e.g., due to low exhaust temperature or low exhaust pressure). As such, the time required for the turbine to spin up and drive the compressor to deliver the required amount of compressed intake air is referred to as turbo lag. During turbo lag, the amount of torque delivered may not match the torque demand, resulting in a drop in engine power.

[0046] As such, during an accelerator pedal depression, when an actual turbine speed is below a desired turbine speed, and when a difference between an intake manifold pressure and an exhaust manifold pressure is less than a threshold difference, the engine may be operated in a secondary air injection mode. The details of engine operation in the secondary air injection mode are described in Fig. 4 is further elaborated upon. Secondary air may, for example, be supplied to the exhaust manifold using a secondary air pump. The amount of secondary air supplied may be based on the desired turbine speed. At the same time, the engine may be operated with a rich in-cylinder air / fuel ratio. As a result of rich engine operation, high levels of CO, H2, and hydrocarbons may be generated from the engine, which may exothermically combine with the secondary air in the exhaust manifold, thereby increasing exhaust energy. The increased exhaust energy may be used to accelerate turbine rotation to the desired speed, thereby reducing turbo lag. During engine operation with secondary air introduction, intake valve timing and exhaust valve timing may be further adjusted to increase the initial torque output.In this way, secondary air injection can be used during an early part of the accelerator pedal depression to accelerate turbine spin-up and increase initial torque output until sufficient boost pressure for blow-by is achieved.

[0047] Upon achieving sufficient boost for blowby (i.e., when the difference between the intake manifold pressure and the exhaust manifold pressure is greater than a threshold difference), the engine may be operated in a combination mode with secondary air injection and blowby until a secondary air injection flow rate is below a threshold flow rate. The details of engine operation in the combination mode are described in Fig. 6. During engine operation in combination mode, for example, the secondary air flow rate may be reduced while an amount of blowby air is increased. Concurrently, the engine may be operated rich to produce rich exhaust gas, which may exothermically combine with secondary air and blowby air in the exhaust manifold to increase exhaust energy. In one example, engine operation may not switch from secondary air introduction mode to combination mode until a threshold boost pressure is reached. The threshold boost pressure may be based, at least for example, on a torque request.

[0048] When the secondary air flow rate falls below the threshold flow rate, secondary air introduction can be stopped and the engine can be operated in a blow-by mode. The details of engine operation in the blow-by mode are described in Fig. 5. For example, during blowby mode, an amount of compressed intake air, also referred to herein as blowby air, may be directed from the intake manifold to the exhaust manifold while maintaining stoichiometric catalyst conditions to provide additional mass flow to spin up the turbine. In some embodiments, fuel injection may be adjusted (e.g., enriched) according to the amount of blowby air to provide additional enthalpy to spin up the turbine. The blowby air may be delivered while the engine has at least some boost, that is, while an intake manifold pressure (MAP) is at least a threshold amount higher than the exhaust manifold pressure.Based on the engine operating conditions prevailing at the time blow-by air is requested, an amount of valve overlap is adjusted so that the required amount of blow-by air can be supplied to the turbine via the engine cylinders through positive valve overlap.

[0049] For example, to provide blowby across the engine cylinders, the VCT system may be adjusted from an initial position with no positive valve overlap to a final position with increased positive valve overlap. In one example, the final position may be a position of full valve overlap (or maximum positive valve overlap). While the methods herein discuss always delivering blowby air via positive valve overlap, in alternative embodiments, blowby air may only be delivered via positive valve overlap if valve timing to provide positive valve overlap does not degrade engine fuel economy, combustion stability, and torque output.

[0050] In one example, engine operation may transition from secondary air injection mode to blow-by mode without operation in combination mode. As an example, a maximum amount of secondary air deliverable by the secondary air pump may be based on ambient pressure. Therefore, at higher altitudes, where ambient pressure is lower, the maximum amount of secondary air deliverable by the secondary air pump may decrease. Consequently, if exhaust pressure increases above a threshold pressure, the amount of secondary air delivered may be significantly less than the desired amount. In other words, the exhaust pressure may exceed the secondary air pump capability. Consequently, engine operation may transition from secondary air injection mode directly to blow-by mode.However, in some examples, the engine may operate in combination mode, where the difference between the actual secondary air amount and the desired secondary air amount is provided via blow-by.

[0051] In another example, engine operation may switch to blow-by mode when conditions for oxidation in the exhaust manifold are not favorable. For example, if an exhaust gas temperature is below a threshold temperature, the secondary air pump may be stopped and the engine may operate in blow-by mode.

[0052] In some examples, heated secondary air may be supplied during engine operation with secondary air injection to increase oxidation in the exhaust manifold.

[0053] In this way, by coordinating the secondary air intake with the blow-by air, turbo lag can be reduced and torque output can be improved. The details of coordinating the secondary air intake with the blow-by air are described with reference to Fig. 3 further elaborated.

[0054] If you Fig. 3, it shows an example routine 300 for determining the type of engine operation performed in response to accelerator pedal depression to reduce turbo lag. For example, during the early part of accelerator pedal depression, when a turbine speed is below a threshold speed and until a threshold boost pressure is reached, secondary air may be introduced into the exhaust manifold to increase exhaust energy that may be used to rotate the turbine. Upon reaching the threshold boost pressure, the secondary air introduction rate may be reduced while simultaneously using blowby. When the secondary air introduction rate decreases below a threshold rate, secondary air introduction may be stopped, and engine operation may switch to a blowby mode, allowing boosted intake air to be directed to the exhaust manifold via positive valve overlap. The method of Fig. 3 can be stored as executable instructions in the non-volatile memory of the Fig. 1-2 shown control unit 120.

[0055] At 302, the method includes estimating and / or measuring engine operating conditions. These may include, for example, engine speed, load, boost, MAP, intake airflow, ambient conditions such as ambient pressure, temperature, humidity, driver torque request, exhaust temperature, turbine speed, boost pressure, pedal position, vehicle speed, engine dilution request, secondary air pump speed, actual secondary air amount, secondary air flow rate, etc. Next, at 304, an accelerator pedal depression may be confirmed. For example, it may be determined if the torque request is increased more than a threshold amount and / or if an accelerator pedal is depressed more than a threshold amount. If no accelerator pedal depression is detected, the routine may end.If the answer at 304 is yes (that is, if an accelerator pedal depression is confirmed), routine 300 may proceed to 306. At 306, the routine may include determining if an actual turbine speed is less than a desired turbine speed. If the answer at 306 is no, the routine may end. If the answer at 306 is yes, the routine may proceed to 308. That is, if the turbine speed is less than the desired speed, the routine may proceed to 308.

[0056] At 308, the routine may include determining whether a difference between a manifold absolute pressure at the intake manifold and an exhaust manifold pressure is greater than a threshold difference. That is, it may be determined whether a positive surge is established. As such, a positive surge may indicate that engine operating conditions are suitable for blowby operation. If the answer at 308 is NO, it may be determined that sufficient boost for the blowby pressure is not available, and then the routine may continue to 310. At 310, the routine may include adjusting engine operation to provide secondary air injection. Upon determining that sufficient boost for blowby is not available, the engine may be operated with secondary air injection, for example.During secondary air injection, a secondary air pump may be operated to supply air to the exhaust manifold, and simultaneously, the engine may be operated with a rich in-cylinder air / fuel ratio to create an exothermic reaction between the exhaust gases from the rich combustion and the secondary air supplied by the secondary air pump. Consequently, the mass and enthalpy of the exhaust gas can be increased, which can be used to increase the turbine speed to the desired turbine speed. Further, during engine operation with secondary air injection, the VCT system may be adjusted to increase the initial torque output. The details of engine operation with secondary air injection are described with reference to FIG. Fig. 4 further elaborated.

[0057] In one example, upon detecting an accelerator pedal entry event when the actual turbine speed is lower than desired, the engine may operate with secondary air injection until a threshold turbine speed is reached, regardless of the difference between intake manifold pressure and exhaust manifold pressure, to improve initial torque output. Upon reaching the threshold turbine speed, engine operation may transition to operation with both secondary air injection and blowby, or blowby alone.

[0058] Returning to 308, if the answer at 308 is yes, the routine may continue to 312. That is, if it is determined that engine operating conditions are suitable for blowby operation, the routine may continue to 312. At 312, the routine may include determining if the secondary air pump is active. If the answer at 312 is yes, the routine may continue to 314. That is, if it is determined that the secondary air pump is active when sufficient boost is available for blowby and the turbine speed is less than desired, the routine may continue to 314. At 314, the routine may include determining if an actual boost pressure is greater than a threshold boost pressure. In this example, the boost pressure may be an intake manifold pressure relative to ambient pressure.The threshold boost pressure may be based on the difference between the intake manifold pressure and the exhaust manifold pressure being greater than the threshold pressure difference, and further based on one or more of the torque request, engine speed, exhaust temperature, engine temperature, etc. For example, upon determining that sufficient boost is available for blowby, engine operation may continue with only secondary air introduction until boost pressure increases above a threshold pressure. Further, as the torque request increases, the threshold boost pressure may increase.

[0059] Accordingly, if the answer at 314 is NO, the routine may continue to 318. At 318, upon determining that the actual boost pressure is less than the threshold boost pressure, the routine may include continuing engine operation with only secondary air introduction.

[0060] If the answer at 314 is YES, the routine may proceed to 322. Upon determining that the actual boost pressure is greater than the threshold boost pressure, the engine may be operated in a combination mode, where secondary air injection and blowby may be performed simultaneously, or a blowby mode, where secondary air injection may be stopped and only blowby may be provided. As such, the type of engine operation that may be performed (when the actual boost pressure is greater than the threshold boost pressure) may be based on an actual secondary air flow rate. Thus, at 322, the routine may include determining whether a secondary air flow rate is less than a threshold rate.

[0061] If at 322, the secondary air flow rate is below the threshold rate, the routine may continue to 324. At 324, the routine may include deactivating the secondary air pump and delivering secondary air only via blow-by. That is, engine operation may switch to blow-by mode when it is determined that the secondary air flow rate is below the threshold rate.

[0062] The amount of blowby may be based on the desired turbine speed. For example, as the desired turbine speed increases, the amount of blowby may increase. The details of engine operation with blowby are described with reference to Fig. 5 further elaborated.

[0063] Returning to 322, if the secondary air flow rate is not less than the threshold rate, the routine may continue to 326. At 326, the routine may include decreasing the secondary air flow rate while increasing the amount of blowby. The amount of blowby may be based on the desired turbine speed and the actual secondary air flow rate. The details of engine operation with secondary air injection and blowby are discussed at Fig. 6 worked out.

[0064] Returning to 312, if the secondary air pump is not active, the routine may continue to 320. At 320, the routine may include operating the engine with blowby to provide secondary air in the exhaust to reduce turbo lag. The amount of blowby may be based on the desired turbine speed. The details of engine operation in blowby mode are discussed with respect to Fig. 5 further elaborated.

[0065] In one example, engine operation may switch from secondary air injection mode to blow-through mode when a desired secondary air injection amount exceeds the secondary air pump capability. For example, an actual secondary air injection amount may be monitored. If the difference between the desired secondary air injection amount and the actual secondary air injection amount is greater than a threshold amount, it may be determined that the secondary air pump is not delivering the desired secondary air injection amount. For example, the secondary air injection amount delivered by the secondary air pump may be based on an ambient pressure and an exhaust pressure. At high altitudes, as the ambient pressure decreases, the amount of secondary air injection delivered by the secondary air pump may decrease. Therefore, the secondary air pump may operate at a higher speed to deliver a desired secondary air injection amount.However, the pump may soon reach maximum speed and the secondary air pump may be unable to supply the desired secondary air injection amount. Therefore, if the difference between the desired secondary air injection amount and the actual secondary air injection amount is above a threshold difference, the secondary air pump may be stopped and additional air for oxidation in the exhaust may be supplied via blowby. For example, if the ambient pressure decreases, blowby may be provided earlier. That is, as altitude increases, the ambient pressure decreases and consequently, blowby may be provided earlier. In one example, the secondary air pump may be stopped earlier in response to a decrease in ambient pressure below a threshold ambient pressure.

[0066] In another example, the secondary air pump may be deactivated based on an exhaust port temperature. For example, if the exhaust port temperature is below a threshold temperature, the exhaust port temperature may be too cold to support sufficient oxidation to generate heat. Therefore, secondary air introduction may be stopped, and the engine may operate in blow-by mode.

[0067] In yet another example, the secondary air pump may be deactivated when an oxidation rate in the exhaust manifold before the turbine is below a threshold rate.

[0068] In this way, engine operation can be coordinated during accelerator pedal depressing to provide secondary air injection prior to providing blowby to reduce turbo lag and improve initial torque output. By providing secondary air injection during an early phase of accelerator pedal depressing, initial torque output can be increased. Furthermore, by utilizing secondary air injection prior to blowby, sufficient boost can be generated for subsequent blowby operation. Consequently, engine performance can be improved.

[0069] In one example, a method for an engine may include, during a first condition, supplying an amount of secondary air upstream of an exhaust turbine only via a secondary air pump; during a second condition, supplying the amount of secondary air via the secondary air pump and supplying an amount of blowby air via positive valve overlap; and during a third condition, supplying only the amount of blowby air via the positive valve overlap. The first condition may include an actual turbine speed less than a desired turbine speed, a difference between an intake manifold pressure and an exhaust manifold pressure less than a threshold pressure difference.The second condition may include an actual turbine speed less than a desired turbine speed, a difference between intake manifold pressure and exhaust manifold pressure greater than the threshold pressure difference, and a boost pressure greater than a threshold boost pressure. The third condition may include an actual turbine speed less than a desired turbine speed, a difference between intake manifold pressure and exhaust manifold pressure greater than the threshold pressure difference, boost pressure greater than the threshold boost pressure, and secondary air amount less than a threshold amount. The third condition may further include deactivating the secondary air pump to stop secondary air flow. Further, a secondary air flow rate based on an amount of oxygen available for oxidation upstream of the turbine may be selected.In some examples, the secondary air pump may be deactivated earlier as altitude increases.

[0070] If you Fig. 4, a routine 400 illustrates a method for adjusting engine operation to supply secondary air via a secondary air pump into the exhaust manifold upstream of a turbine to reduce a duration required to increase a speed of the turbine to a desired turbine speed during transient conditions such as an accelerator pedal depression. In particular, the secondary air pump may be used to supply secondary air during an early portion of the accelerator pedal depression when sufficient boost is not available for a blow-by operation. The method of Fig. 4 can be stored as executable instructions in the non-volatile memory of the Fig. 1-2 shown control unit 120.

[0071] At 402, routine 400 may include determining and / or measuring engine operating conditions. The engine operating conditions may include an engine temperature, an engine speed, an engine load, an ambient temperature, a barometric pressure, an exhaust temperature, a secondary air pump speed, a secondary air amount, an accelerator pedal position, a battery state of charge, etc. Next, at 404, routine 400 may include determining a desired turbine speed. The desired turbine speed may be based, for example, on a torque request and an accelerator pedal position. After determining the desired turbine speed, the routine may continue to 406. At 406, the routine may include determining a desired secondary air injection flow rate based on the desired turbine speed.For example, as the desired turbine speed increases, the desired secondary air injection flow rate may increase.

[0072] Next, at 408, the routine includes adjusting the secondary air pump to supply a desired amount of secondary air. For example, a speed of the secondary air pump may be adjusted to supply the desired amount of secondary air. After adjusting the secondary air pump, at 410, the routine includes determining an actual secondary air flow rate. The actual secondary air flow rate may be based, for example, on the secondary air pump speed, ambient pressure, and exhaust pressure.

[0073] Next, at 412, routine 400 includes adjusting engine operation based on the actual secondary air flow rate. For example, at 414, adjusting engine operation includes adjusting a fuel injection amount based on the actual secondary air flow rate. In one example, the fuel injection amount may increase as the secondary air flow rate increases. Further, the fuel injection amount may be adjusted such that the overall engine air / fuel ratio is stoichiometric. Consequently, when secondary air injection is used, the engine may operate with a rich in-cylinder air / fuel ratio. Further, at 416, adjusting engine operation may include adjusting the VCT system so that volumetric efficiency may be optimized.For example, intake and / or exhaust valve timing may be adjusted to reduce positive valve overlap and increase initial torque output. Still further at 418, adjusting engine operation may include adjusting spark timing. For example, during engine operation in secondary air introduction mode, spark timing may be retarded. An amount of spark retard may be based on one or more of a desired torque output and a desired exhaust energy to the turbine. However, an amount of spark retard provided during secondary air introduction may be less than the amount of spark retard provided during blowby. Because less spark retard may be used during secondary air introduction, combustion may occur near the optimum for immediate torque output.Consequently, the initial torque output can be increased when secondary air injection is used.

[0074] In this way, secondary air injection can be used early during accelerator pedal depressing to increase initial torque output, generate sufficient boost for blow-by operation, and reduce turbo lag.

[0075] If you now look Fig. 5, routine 500 illustrates a blow-by method to reduce turbo lag. The method of Fig. 5 can be stored as executable instructions in the non-volatile memory of the Fig. 1-2. In response to an accelerator pedal depression, for example, the engine 100 may initially operate with secondary air injection (as shown in Fig. 4) to create boost for blowby, accelerate turbine rotation to a desired speed, and increase initial torque output. Subsequently, engine operation may switch to provide blowby only when a secondary air injection amount decreases below a threshold injection amount. In some examples, blowby may be provided in response to accelerator pedal depressing when a difference between intake manifold pressure and exhaust manifold pressure increases above a threshold difference. In some other examples, blowby may be provided in response to accelerator pedal depressing when a boost pressure is at or above a threshold boost pressure. Before reaching the threshold boost pressure, the engine may operate with secondary air injection, as in Fig. 4 discussed.

[0076] As such, during blowby, the engine can be operated with positive overlap, allowing the boosted blowby air to be directed into the engine exhaust. Furthermore, the engine can be operated with a rich cylinder air / fuel ratio. The blowby air can react exothermically with the engine exhaust gas (generated by rich combustion) in the exhaust manifold, increasing the mass and enthalpy of the exhaust gas to increase the turbine speed to the desired speed.

[0077] At 502, routine 500 may include determining and / or measuring engine operating conditions. The engine operating conditions may include engine speed, a desired torque output, an exhaust temperature, an exhaust catalyst temperature, a turbine speed, an intake manifold pressure, a boost pressure, a barometric pressure, an exhaust manifold pressure, a pedal position, a vehicle speed, etc. After determining the engine operating conditions, the routine may proceed to 504 to determine a desired turbine speed. The desired turbine speed may be based on, for example, a torque request and an accelerator pedal position.

[0078] Next, at 504, the routine may include determining a desired blow-by amount based at least on the desired turbine speed. For example, as the desired turbine speed increases, the blow-by amount may increase.

[0079] After determining the desired blowby amount, routine 500 may include, at 508, adjusting engine operation based on the desired blowby amount. Adjusting engine operation may include, for example, at 510, adjusting intake valve timing and exhaust valve timing to create positive valve overlap between an intake valve and an exhaust valve. In particular, exhaust valve closing may be delayed and intake valve opening may be advanced to create positive valve overlap for blowby scavenging. Further, the duration of the positive overlap, an intake valve lift amount, and an exhaust valve lift amount may be adjusted to create the desired blowby.Further, adjusting engine operation at 512 may include adjusting a fuel injection amount proportional to the blowby amount to maintain an overall stoichiometric engine air / fuel ratio. The fuel injection amount may be adjusted, for example, by adjusting a fuel injector pulse width. Still further, at 514, spark timing may be adjusted. For example, the spark timing may be retarded as the amount of blowby increases.

[0080] In this way, blow-by air can be provided during a later part of the accelerator pedal depression after the secondary air introduction to increase the turbine speed to the desired turbine speed.

[0081] If you Fig. Turning to Figure 6, a routine 600 illustrates a method for supplying a combination of secondary air and blowby such that secondary air from a secondary air pump and the boosted air from a blowby operation in the exhaust manifold are available simultaneously to reduce turbo lag. The method of Fig. 6 can be stored as executable instructions in the non-volatile memory of the Fig. 1-2. For example, during an accelerator pedal depression, secondary air injection may be performed until an actual boost pressure reaches a threshold boost pressure, after which the engine may operate with secondary air injection and blowby before switching to blowby-only operation to decrease a time period to increase an actual turbine speed to a desired turbine speed. In other words, during an early phase of the accelerator pedal depression, the engine may operate with only secondary air injection, during an intermediate phase of the accelerator pedal depression, the engine may operate with secondary air injection and blowby, and during a late phase of the accelerator pedal depression, the engine may operate with only blowby.

[0082] In principle, the intermediate phase of engine operation can be performed with secondary air injection and blow-through to transition engine operation from only secondary air injection to only blow-through. As the intermediate phase progresses, the secondary air injection amount can be reduced and the blow-through amount can be increased.

[0083] At 602, routine 600 may include determining and / or measuring engine operating conditions. The engine operating conditions may include engine temperature, engine speed, engine load, ambient temperature, barometric pressure, exhaust temperature, exhaust catalyst temperature, secondary air pump speed, secondary air quantity, battery state of charge, exhaust air / fuel ratio, etc.

[0084] Next, at 604, routine 600 may include determining a desired turbine speed. The desired turbine speed may be based, for example, on a torque request and an accelerator pedal position. After determining the desired turbine speed, the routine may proceed to 606.

[0085] At 606, the routine may include determining an actual secondary air flow rate. Prior to operation with blow-by and secondary air injection, the engine itself may be operated with only secondary air injection.

[0086] Next, at 607, the routine may include decreasing the secondary air flow rate by a threshold rate. The secondary air flow rate may be decreased, for example, by decreasing a secondary air pump speed. In one example, the threshold rate may be a fixed rate. In another example, the threshold rate may increase with each engine cycle. After decreasing the secondary air flow rate, routine 600 may proceed to 608. At 608, the routine may include determining a desired blowby amount based at least on the desired turbine speed and the decreased secondary air flow rate. For example, as the secondary air injection rate decreases, the blowby amount may increase.

[0087] Next, at 610, routine 600 includes adjusting engine operation to provide blowby based on the desired blowby amount. Adjusting engine operation to provide blowby may include, at 612, adjusting a fuel injection amount based on the desired turbine speed, the reduced secondary air injection amount, and the desired blowby amount. As such, the engine may be operating rich when creating secondary air and blowby to provide CO, H2, and hydrocarbons from the engine into the exhaust manifold. These compounds from the rich combustion event may exothermically react with secondary air from the secondary air pump and the blowby air to provide additional exhaust energy to accelerate turbine rotation to the desired turbine speed.

[0088] At 614, engine operation may include adjusting intake valve timing and exhaust valve timing to create positive overlap. For example, exhaust valve closing timing may be retarded and intake valve opening timing may be advanced to create positive valve overlap. Further, the duration of the positive overlap, an intake valve lift amount, and an exhaust valve lift amount may be adjusted to create the desired blowby.

[0089] At 616, engine operation may include adjusting VCT response timing based on the rate of change of secondary air injection. Further, at 618, spark timing may be adjusted. For example, spark timing may be retarded and the amount of spark retard may increase as the desired amount of air for oxidation in the exhaust increases.

[0090] In this way, during accelerator pedal depressing, the engine can be operated in a combination mode with secondary air introduction and blow-by after operation in secondary air mode and before operation in blow-by mode to reduce turbo lag.

[0091] If you Fig. 7, example settings of the secondary air introduction and blow-through during an accelerator pedal operation are shown. The sequence of Fig. 7 can be executed by executing commands in the system of Fig. 1 according to the procedure of Fig. 3-6. Vertical markers at times t0-t3 represent times of interest during the sequence. In all graphs discussed below, the x-axis represents time, and time increases from the left side of each graph to the right side of each graph.

[0092] The first diagram from the top of Fig. Figure 7 represents the accelerator pedal position (PP) as a function of time. The Y-axis represents the accelerator pedal position, and depressing the accelerator pedal increases in the direction of the Y-axis arrow.

[0093] The second diagram from the top of Fig. 7 represents the turbine speed as a function of time. The Y-axis represents a turbine speed, and the turbine speed increases in the direction of the Y-axis arrow. Curve 704 represents a desired turbine speed, curve 706 represents an actual turbine speed, and horizontal line 708 represents a threshold turbine speed. As such, the threshold speed may be a turbine speed at which sufficient boost pressure can be generated for blowby.

[0094] The third diagram from the top of Fig. 7 illustrates boost pressure as a function of time. The Y-axis represents boost pressure, and boost pressure increases in the direction of the Y-axis arrow. Curve 710 represents a desired boost pressure, curve 712 represents an actual boost pressure, and horizontal line 714 represents a threshold boost pressure. As such, at threshold boost pressure, a difference between an intake manifold pressure and an exhaust manifold pressure may reach a pressure equal to or greater than a threshold pressure difference required to generate the boost pressure to create blowby.

[0095] The fourth diagram from the top of Fig. 7 represents the secondary air introduction amount as a function of time. The Y-axis represents a secondary air introduction amount, and the secondary air introduction amount increases in the direction of the Y-axis arrow.

[0096] The fifth diagram from the top of Fig. 7 represents the blow-by rate as a function of time. The Y-axis represents a blow-by rate, and the blow-by rate increases in the direction of the Y-axis arrow.

[0097] The sixth diagram from the top of Fig. Figure 7 represents the in-cylinder air / fuel ratio as a function of time. The Y-axis represents the in-cylinder air / fuel ratio, and the richness of the in-cylinder air / fuel ratio increases in the direction of the Y-axis arrow. The X-axis represents time, and time increases from the left side of the graph to the right side of the graph. The horizontal line 722 represents a stoichiometric air / fuel ratio.

[0098] As such, the desired turbine speed may be based on one or more of a torque request and an accelerator pedal position, the desired boost pressure may be based on one or more of a torque request and an accelerator pedal position, the secondary air injection amount may be based on the desired turbine speed and the blowby amount may be based on the desired turbine speed when only blowby is provided, and based on the desired turbine speed and the actual secondary air flow rate when both blowby and secondary air injection are provided.

[0099] At the time before t1, the engine may be operating at low engine speed and low load conditions. The difference between the desired turbine speed and the actual turbine speed may be no greater than a threshold speed. Likewise, the difference between the desired boost and the actual boost pressure may be no greater than a threshold pressure. In one example, the actual turbine speed may reach the desired turbine speed and the actual boost may reach the desired boost. Therefore, additional secondary air may not be required to increase the turbine speed to achieve a desired boost. That is, the engine may be operating in a normal mode with no blowby and no secondary air introduction. Further, the engine may be operating at a stoichiometric air / fuel ratio.

[0100] At time t1, an accelerator pedal depression may be detected. The accelerator pedal depression may be detected, for example, based on one or more of an increase in torque request greater than a threshold request and an increase in accelerator pedal position (depression) greater than a threshold amount. Between times t1 and t2, in response to the detection of the accelerator pedal depression, the desired boost pressure may increase (710). To provide the desired boost, the desired turbine speed may increase (704). However, the actual turbine speed (706) may be less than the desired turbine speed (704). Consequently, the actual boost (712) may be less than the desired boost (710).Furthermore, the difference between the desired turbine speed and the actual turbine speed may be greater than a threshold speed difference, and the difference between the desired boost pressure and the actual boost pressure may be greater than a threshold boost pressure difference. This means that the engine may experience turbo lag.

[0101] To reduce turbo lag, the engine may be operated in a secondary air injection mode at t1. That is, to reduce a time period to increase the actual turbine speed to the desired speed, and therefore reduce a time period to increase the actual boost to the desired boost, the engine may be operated in the secondary air injection mode. As such, during the initial phase of accelerator pedal depression, a difference between an intake manifold pressure and an exhaust manifold pressure may not be greater than a threshold manifold pressure difference (not shown). Consequently, a sufficient pressure difference may not be available to provide blow-by air in the exhaust manifold. Therefore, a secondary air pump (e.g., the air pump 96 in Fig. 1) are used to introduce secondary air into the exhaust manifold upstream of the turbine. The details of engine operation with secondary air injection are described in Fig. 4. An amount of secondary air introduced into the exhaust manifold (716) may be based on the desired turbine speed. For example, as the desired turbine speed increases, the amount of secondary air introduced may increase. In one example, the amount of secondary air introduced may be based on the desired exhaust energy required to increase the turbine speed to the desired speed.

[0102] Furthermore, the engine may be operated with a rich in-cylinder air / fuel ratio between times t1 and t2. The degree of richness may be based on the amount of secondary air injection. In one example, the amount of fuel injection may be based on the amount of secondary air injection. When the cylinder is operated with a rich air / fuel ratio, high levels of carbon monoxide (CO), hydrogen (H2), and hydrocarbons may be generated from the engine, which may react exothermically with the secondary air introduced into the exhaust manifold. Consequently, the mass and enthalpy of the exhaust gases may be increased. The increased exhaust energy may be used to shorten the time it takes for the turbine to reach the desired speed. In other words, by utilizing secondary air injection and in-cylinder enrichment during an initial phase of accelerator pedal depressing, turbo lag may be reduced.Furthermore, by providing secondary air, the trapped mass of compressed intake air in the cylinder can increase, resulting in increased initial torque output relative to normal engine operation when secondary air injection is not used. Even further, valve timing can be adjusted for increased volumetric efficiency to increase initial torque output during accelerator pedal depressing.

[0103] At time t2, the actual turbine speed (706) may reach a threshold speed (708) and the actual boost pressure may reach a threshold pressure. However, the actual turbine speed may still be below the desired turbine speed and the boost pressure may still be below the desired boost pressure. Further, at t2, the difference between the intake manifold pressure and the exhaust manifold pressure may be at a threshold pressure difference at which sufficient boost may be available to provide blowby. Consequently, engine operation may switch from delivering only secondary air via the secondary air pump to using a combination of secondary air injection and blowby.In one example, during accelerator pedal depressing, when the actual boost pressure reaches the threshold boost pressure, engine operation may switch from using the secondary air pump for secondary air to providing blowby via positive valve overlap. In another example, during accelerator pedal depressing, as shown in the example presented here, when the actual boost pressure reaches the threshold boost pressure, engine operation may switch from using the secondary air pump for secondary air to using both secondary air and blowby. However, in some examples, the threshold pressure differential required for blowby may be reached earlier than the threshold boost pressure.Thus, in one example, upon reaching the threshold pressure differential required for blowby, the engine may continue to use only the secondary air pump for secondary air until the threshold boost pressure is reached, at which engine operation may either switch to a combination of using the secondary air pump and blowby or switch to a blowby-only mode.

[0104] Between times t2 and t3, the turbine speed may increase above the threshold speed and the boost pressure may increase above the threshold pressure. As such, sufficient boost may be available for blowby. Consequently, the engine may be operated with secondary air injection and blowby. For example, the secondary air injection amount may be reduced and blowby increased for a period of time until the secondary air injection amount falls below a threshold amount. As such, the secondary air may be supplied to the exhaust manifold upstream of the turbine by the secondary air pump. Blowby may be provided by adjusting valve timing so that the intake and exhaust valves have a duration of positive overlap. The details of engine operation in combination mode, during which secondary air injection and blowby are provided simultaneously, are described in Fig. 6. Further, the engine may be operated with a rich in-cylinder air / fuel ratio. The fuel injection amount may be based on the secondary air injection amount, a blow-by amount, and the desired turbine speed. In one example, the fuel injection amount may be based on the secondary air injection amount, the blow-by amount, the desired turbine speed, and / or the desired torque request.

[0105] At time t3, the secondary air injection amount may decrease below a threshold injection amount. Consequently, engine operation may switch from using both secondary air injection and blowby to using only blowby until the desired turbine speed is reached.

[0106] At times between t3 and t4, engine operation can continue with blowby only. As such, during blowby, the positive overlap between the intake and exhaust valves can be provided to deliver boosted air from the intake directly into the exhaust manifold. Furthermore, the cylinder can operate with a rich in-cylinder air / fuel ratio. The unburned fuel in the exhaust gas can combine exothermically with the blowby air. Consequently, the mass and enthalpy of the exhaust gas can be increased. Consequently, turbine rotation can be accelerated to the desired speed, and turbo lag can be reduced.

[0107] At time t4, the actual turbine speed may reach the desired turbine speed and the boost pressure may reach the desired boost pressure. Consequently, the desired torque request may be met. Upon reaching the desired turbine speed and / or torque request, blowby may be stopped. That is, upon reaching, engine operation may transition from providing blowby to normal engine operation without secondary air introduction and / or blowby. Engine operation in normal mode may include, for example, providing no positive overlap or minimal positive overlap such that no blowby air is provided (or blowby may be negligible), and not operating the secondary air pump. Further, during engine operation in normal mode, the in-cylinder air / fuel ratio may be maintained at stoichiometry.

[0108] In this manner, in response to an accelerator pedal depression, the engine may be operated with only secondary air introduction during an early portion of the accelerator pedal depression, with secondary air introduction and blow-by during an intermediate portion of the accelerator pedal depression, and with only blow-by during a later portion of the accelerator pedal depression to improve initial torque output and reduce turbo lag.

[0109] In one example, a method may include: supplying compressed air through a throttle to an engine from a compressor driven by a turbine coupled to an exhaust of the engine; and during an accelerator pedal depression of the throttle, reducing turbo lag by supplying ambient air to the turbine during a first operating mode and, during a second operating mode, providing blow-by of a portion of the compressed air through the engine to the turbine without combustion. During the accelerator pedal depression, the engine may further operate in a third operating mode that simultaneously includes supplying ambient air to the turbine and providing blow-by of a portion of the compressed air through the engine to the turbine without combustion.The first operating mode occurs when a pressure difference between the air pressure downstream of the throttle and the exhaust gas pressure is less than a first threshold. The second operating mode occurs when a pressure difference between the air pressure downstream of the throttle and the exhaust gas pressure exceeds a second threshold. Further, ambient air is supplied by an air pump coupled to the exhaust upstream of the turbine, and blowby is provided during an exhaust stroke of a combustion chamber of the engine by opening an intake valve coupled to the combustion chamber prior to closing an exhaust valve coupled to the combustion chamber.Still further, the first mode of operation continues until the boost pressure from the compressor reaches a preselected amount and may include adjusting the fuel injection amount based on an amount of ambient air supplied, wherein the amount of ambient air supplied is based on a desired turbine speed. During the second mode, adjusting the fuel injection amount may be based on an amount of blowby provided, and during the third mode, adjusting the fuel injection amount may be based on the amount of ambient air and the amount of blowby.

[0110] Still further, the first mode may include setting a first spark timing, the second mode may include setting a second spark timing, and the third mode may include setting a third spark timing, wherein the first spark timing is retarded less than the third spark timing and the third spark timing is retarded less than the second spark timing. By setting the first spark timing less than the third spark timing, the spark timings may be adjusted for increased initial torque output while increasing exhaust energy to reduce turbo lag.

[0111] It should be noted that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. As such, various illustrated acts, operations, or functions may be performed in parallel in the illustrated sequence, or in some cases, omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of explanation and description.One or more of the illustrated actions or functions may be performed repeatedly depending on the specific strategy used. Furthermore, the described actions may graphically represent code to be programmed into the computer-readable storage medium in the engine control system.

Claims

[1] Procedure comprising: Supplying compressed air through a throttle valve to an engine from a compressor driven by a turbine coupled to an exhaust of the engine; and while depressing an accelerator pedal to adjust the throttle valve, reducing turbo lag by supplying ambient air to the turbine during a first operating mode and, during a second operating mode, providing blow-through of a portion of the compressed air through the engine to the turbine without combustion, further comprising a third operating mode which simultaneously comprises supplying ambient air to the turbine and providing blow-through of a portion of the compressed air through the engine to the turbine without combustion, wherein the first operating mode occurs when a pressure difference between the air pressure downstream of the throttle valve and the pressure of the exhaust gas is less than a first threshold value, and wherein the second operating mode occurs when a pressure difference between the air pressure downstream of the throttle valve and the pressure of the exhaust gas exceeds a second threshold. [2] The method of claim 1, wherein the ambient air is supplied by an air pump coupled to an outlet upstream of the turbine. [3] The method of claim 1, wherein the blowby is provided during valve overlap of a combustion chamber of the engine by opening an intake valve coupled to the combustion chamber prior to closing an exhaust valve coupled to the combustion chamber. [4] The method of claim 1, wherein the first mode of operation continues until the boost pressure downstream of the compressor reaches a preselected amount. [5] The method of claim 1, further comprising, during the first mode, adjusting a fuel injection amount based on an amount of ambient air supplied, during the second mode, adjusting the fuel injection amount based on an amount of blowby provided, and during the third mode, adjusting the fuel injection amount based on the amount of ambient air and the amount of blowby. [6] The method of claim 5, wherein the amount of ambient air supplied is based on a desired turbine speed. [7] The method of claim 6, further comprising during the first mode adjusting a first spark timing, during the second mode adjusting a second spark timing, and during the third mode adjusting a third spark timing, wherein the first spark timing is retarded less than the third spark timing and the third spark timing is retarded less than the second spark timing. [8] A method for a prime mover comprising: during a first condition, supplying an amount of secondary air upstream of a turbine coupled to an exhaust of the engine only via a secondary air pump; during a second condition, supplying the secondary air quantity via the secondary air pump and supplying a blow-by air quantity via a positive valve overlap of an intake valve and an exhaust valve of the engine; and during a third condition supplying only the blow-through air quantity via the positive valve overlap, wherein the first condition comprises one or more of the following: an actual turbine speed that is less than a desired turbine speed, a difference between the pressure in an intake manifold of the engine and the pressure in an exhaust manifold of the engine that is less than a threshold pressure difference, wherein the second condition comprises one or more of the following: the actual turbine speed being less than the desired turbine speed, a difference between the intake manifold pressure and the exhaust manifold pressure being greater than the threshold pressure difference, and a boost pressure being greater than a threshold boost pressure, wherein the third condition comprises one or more of the following: the actual turbine speed being less than the desired turbine speed, the difference between the intake manifold pressure and the exhaust manifold pressure being greater than the threshold pressure difference, the boost pressure being greater than the threshold boost pressure, and a secondary air amount being less than a threshold amount, [9] The method of claim 8, further comprising adjusting a secondary air flow rate based on an amount of oxygen available for oxidation upstream of the turbine and wherein the boost pressure is an intake manifold pressure. [10] The method of claim 9, further comprising, during the third condition, deactivating the secondary air pump to stop the secondary air flow. [11] The method of claim 10, further comprising deactivating the secondary air pump earlier with increasing altitude. [12] A method for a prime mover comprising: while depressing an accelerator pedal to adjust a throttle valve coupled to an intake manifold of the engine, when a boost pressure from a compressor coupled to the intake manifold is less than a threshold boost pressure, operating the engine in a secondary air introduction mode to provide a desired secondary air flow rate to a turbine coupled to an exhaust of the engine, the turbine driving the compressor; and when the boost pressure is greater than the threshold boost pressure, operating the engine in a combination mode to provide blow-by of a portion of the compressed air from the compressor to the turbine in addition to operating the engine in the secondary air injection mode; wherein during the secondary air introduction mode, the desired secondary air flow rate is based on a desired turbine speed; and wherein during the combination mode the secondary air flow rate is reduced and a blow-through amount is increased. [13] The method of claim 12, further comprising, when the secondary air flow rate is below a threshold flow rate, deactivating the secondary air introduction mode and operating the engine in the blow-through mode, wherein deactivating the secondary air introduction mode comprises stopping a secondary air pump. [14] The method of claim 12, further comprising, in response to a difference between the desired secondary air flow rate and an actual secondary air flow rate increasing above a threshold flow rate difference, and in response to the secondary air introduction flow rate being below a threshold flow rate, stopping the secondary air introduction and providing boosted air in the exhaust manifold via blow-by.

Images