Method and system for boosting an engine

Abstract

The present invention relates to methods and systems for boosting an engine. Methods and systems are provided for coordinated control of a compound boost system including a first compressor staged upstream of a second compressor in an engine intake. In one example, the method includes: operating the second downstream compressor at steady state to achieve a total pressure ratio across the compound boost system while transiently operating the first upstream compressor based on insufficient air flow at the downstream compressor. When the pressure ratio across the second compressor changes, dynamically adjusting the timing and amount of electric assistance provided for transiently operating the first upstream compressor.

Description

Technical Field

[0001] The present description generally relates to methods and systems for a boosted engine system having a staged supercharging arrangement. Background Art

[0002] The engine may be configured with a boost device, such as a turbocharger or a supercharger, to increase the air flow into the combustion chamber. Turbochargers and superchargers use an intake compressor to compress the intake air entering the engine. A turbocharger includes a compressor driven mechanically by an exhaust turbine, while an electric supercharger includes a compressor driven electrically by a motor. In some engine systems, one or more intake boost devices may be staged in series or in parallel at what may be referred to as a compound boost configuration. For example, a fast auxiliary boost device (e.g., an electric supercharger) may be used to increase the transient performance of a slower main boost device (e.g., a turbocharger). In such a configuration, the size of the turbocharger may be increased to increase the peak power and torque performance of the engine, which enables a more aggressive reduction in the size of the engine.

[0003] Various schemes can be used to provide boost control in a compound boost system. An example scheme using a pressure ratio for a compound boost control system is shown in EP1,927,739A1 by Petrovic et al. The pressure ratio may represent the boost capability of the boost device of the compound boost system. In Petrovic's scheme, a method for coordinating two turbochargers based on a desired partial pressure ratio is disclosed. Specifically, the desired partial pressure ratio of each turbocharger is determined based on a calibrated lookup table using the engine speed and engine torque as inputs. The desired partial pressure ratio is then achieved by at least one of the following: adjusting the turbocharger wastegate opening, adjusting the turbine blade geometry (for example, if a variable geometry turbine is included), and adjusting the opening of the turbine and / or compressor bypass.

[0004] However, the inventors have recognized potential problems with such systems. As an example, using a predefined calibration to determine the desired partial pressure ratio is a static solution, and the desired partial pressure ratios may be independent of each other (e.g., the desired partial pressure ratio of one compression device does not affect the desired partial pressure ratio of another compression device). If Petrovic's solution is applied to a compound boost system including an electric supercharger staged in parallel with a turbocharger, the solution may cause the supercharger to run for a longer duration than required, causing a decrease in fuel economy. As another example, the pressure ratio commanded to each compression device may be conservatively calibrated to minimize boost pressure overshoot. However, this can result in a slower boost response. Further, if any compression device is configured with electric assistance (such as electric assistance from an electric motor / generator connected to a supercharger compressor, a turbocharger compressor, or a turbocharger shaft), opening the exhaust wastegate in response to boost pressure overshoot may represent an opportunity for energy recovery lost at the electric motor / generator. Summary of the invention

[0005] In one example, the above problem can be solved by the following method, which includes: adjusting the operation of the first intake compression device based on the target boost pressure; when the difference between the throttle inlet pressure and the target boost pressure is higher than a threshold, commanding a positive torque from the electric motor to the second intake compression device; and when the difference is less than the threshold, commanding a negative torque from the electric motor to the second intake compression device. In this way, the target boost pressure can be reached faster while increasing the energy recovery opportunities of the electric motor.

[0006] As an example, a compound boost system may include an upstream faster acting auxiliary compressor (e.g., an electric supercharger compressor) configured with electric assistance and a downstream slower acting main compressor (e.g., a turbocharger compressor). In response to an operator torque demand, an engine controller may dynamically assign a pressure ratio to each compressor to provide a target boost pressure. In particular, a total pressure ratio command for a turbocharger may be actively generated. The total pressure ratio command may include a corresponding adjustment of the opening of an exhaust wastegate valve in a wastegate coupled to both ends of a turbocharger turbine. For example, as torque demand increases, the wastegate opening may be more actively reduced to direct more exhaust gas to flow through the turbine, speeding up the rotation of the turbine to speed up the rotation of the turbocharger compressor. However, due to the inherently slower response time of the turbocharger, there may be a temporary shortfall in boost availability, as indicated by a difference above a threshold between the target boost pressure and the throttle inlet pressure (or the outlet pressure of the turbocharger compressor). This shortfall may be addressed by using positive torque from an electric motor to speed up the rotation of the electric supercharger. When the deficit decreases, such as when there is a difference between the target boost pressure and the throttle inlet pressure below a threshold, but before the throttle inlet pressure reaches the target boost pressure, the electric assist may be disabled and the motor may be used as a generator to absorb torque from the compressor. By adjusting the timing of when the electric assist is disabled, the throttle inlet pressure may coast toward the target boost pressure without incurring any overshoot, while energy can be recovered at the electric motor. It should be appreciated that while this example is described with reference to an electric supercharger, it is not meant to be limiting and the same approach may be used with alternative compression devices configured with electric assist, such as an electric turbocharger.

[0007] In this way, by more aggressively calibrating the pressure ratio commanded to each of the higher frequency auxiliary compressor configured with electric assistance and the lower frequency main compressor, the target boost pressure can be achieved more efficiently. When the actual boost pressure is farther from the target boost pressure, by commanding a positive speed output to the electric motor providing the electric assist, the transient boost response can be improved. When the actual boost pressure is closer to but has not yet reached the target boost pressure, the technical effect of commanding a negative speed output to the electric motor is to reduce boost overshoot while maximizing the energy recovery capability of the electric motor. Overall, the boost pressure can be provided quickly and more efficiently.

[0008] It should be understood that the above summary is provided to introduce selected concepts in a simplified form, which will be further described in the detailed description. This is not meant to establish key or essential features of the claimed subject matter, the scope of which is solely defined by the appended claims. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An example embodiment of a compound boost engine system having a multi-stage intake air compression arrangement is shown.

[0010] Figure 2 A high level flow chart is described for dynamically allocating pressure ratios between each of a plurality of intake compression devices in a compound boost engine system and regulating motor torque delivery to an intake compression device configured with electric assist using a lead compensator.

[0011] Figure 3 An example dynamic pressure ratio distribution between electric supercharger and turbocharger control during a vehicle acceleration event is described.

[0012] Figure 4 Describe an example system response using a lead compensator.

[0013] Figure 5 An example block diagram depicting a boost control architecture including dynamic pressure ratio allocation and lead compensation capabilities.

[0014] Figure 6 An example method of boost control by coordinating operation of a turbocharger and an electric supercharger using dynamic pressure ratio distribution and lead compensation is described.

[0015] Figure 7 A map with example acceleration trajectories according to the present disclosure is shown.

[0016] Figure 8 A prophetic example of turbocharger and electric supercharger pressure ratio coordination during vehicle operation is described. DETAILED DESCRIPTION

[0017] The following description relates to systems and methods for boost control in an engine system having a staged boost device, wherein at least one of the boost devices is configured with electric assist. Figure 1 A non-limiting example of such a boosted engine system is shown in FIG, where a turbocharger is staged downstream of an electric supercharger. Boost control in a compound boost system may be achieved by dynamically assigning different pressure ratio commands to each compression device, and by further using lead compensation to reduce pressure overshoot. The engine controller may be configured to Figure 5 The control architecture executes control programs (such as Figure 2 ) to distribute the pressure ratio to the slower acting compression device based on torque demand, while distributing the pressure ratio to the faster acting compression device (which has electric assist) based on insufficient air flow. In addition, the controller may use a lead compensator to determine when to increase and decrease the electric assist from the electric motor in order to reduce pressure overshoot. Figure 6The example program shown here can be applied to Figure 1 An example solution in an engine system. Figure 3 As shown, due to the dynamic pressure ratio distribution, the target boost pressure can be achieved in a shorter time and with reduced reliance on electric assistance. Figure 4 As shown, due to the lead compensation, the boost pressure overshoot can be reduced while maximizing the energy recovery opportunities at the electric motor. By relying on these schemes, it is possible to improve the acceleration trajectory, such as Figure 7 As shown in Figure 8 A prophetic example of coordinating turbocharger and electric supercharger operation based on pressure ratio during vehicle operation is shown in FIG.

[0018] Figure 1 Aspects of an example engine system 100 are schematically shown, which includes an engine 10 coupled to a vehicle 102. In some examples, the vehicle 102 may be a hybrid vehicle having multiple torque sources that can be used for one or more wheels 47. In other examples, the vehicle 102 is a conventional vehicle with only an engine. In the illustrated example, the powertrain of the vehicle 102 includes the engine 10 and the motor 52. The motor 52 may be a motor or a motor / generator (M / G). When one or more clutches 53 are engaged, the engine 10 and the motor 52 are connected to the wheels 47 via the transmission 48. In the depicted example, the (first) clutch 53 is disposed between the engine 10 and the motor 52, and the (second) clutch 53 is disposed between the motor 52 and the transmission 48. The controller 12 may send a signal to the actuator of each clutch 53 to engage or disengage the clutch, thereby connecting or disconnecting the engine 10 with the motor 52 and components connected thereto, and / or connecting or disconnecting the motor 52 with the transmission 48 and components connected thereto. For example, when clutch 53 is engaged, torque from engine 10 can be transmitted to wheels 47 via crankshaft 40, transmission 48, and driveline shaft 84. Transmission 48 can be a gearbox, planetary gear system, or other type of transmission. Transmission 48 can be a fixed ratio transmission that includes multiple gear ratios to allow engine 10 to rotate at a different speed than wheels 47. By varying the torque transmission capacity of first clutch 53 (e.g., the amount of clutch slip), the amount of engine torque relayed to the wheels via driveline shaft 84 can be adjusted.

[0019] The powertrain system can be configured in various ways, including parallel, series, or series-parallel hybrid vehicles. In an electric vehicle embodiment, the system battery 45 can be a traction battery that delivers power to the motor 52 to provide torque to the wheels 47. In certain embodiments, the motor 52 can also be operated as a generator to provide power to charge the system battery 45, for example, during braking operations. It should be understood that in other embodiments, including non-electric vehicle embodiments, the system battery 45 can be a typical starting, lighting, ignition (SLI) battery coupled to an alternator (ALT) 46.

[0020] The alternator 46 can be configured to charge the system battery 45 using engine torque drawn from the crankshaft during engine operation. In addition, as further described below, the alternator 46 can power one or more electrical systems of the engine (such as one or more auxiliary systems including a heating, ventilation, and air conditioning (HVAC) system, lights, an in-vehicle entertainment system, and other auxiliary systems) based on their corresponding electrical needs. In one example, the current drawn on the alternator can be continuously varied based on each of the following: cabin cooling needs, battery charging needs, other auxiliary vehicle system needs, and motor torque. A voltage regulator can be coupled to the alternator 46 to regulate the power output of the alternator based on system usage needs (including auxiliary system needs).

[0021] In the depicted embodiment, the engine 10 is a compound boost engine configured with a plurality of staged boost devices. Specifically, the engine 10 includes a first boost device that is staged upstream of a second boost device. Here, the first boost device is an auxiliary boost device, and the second boost device is a main boost device, although other configurations are also possible. The depicted configuration causes the first compressor 110 (of the first boost device) to be positioned in the engine intake passage 42 upstream of the second compressor 114 (of the second boost device). At least one of the boost devices may be configured with electric assistance from an electric motor. In this example, the first boost device is an electric supercharger 13 configured to operate with electric assistance from an electric motor, and the second boost device is a turbocharger 15. However, other combinations and configurations of boost devices are also possible without departing from the scope of the present disclosure. For example, in an alternative embodiment, the turbocharger 15 may be an electric turbocharger having an electric motor coupled to a compressor, a turbine, or a turbocharger shaft, and the supercharger is configured as an electric supercharger or a mechanical supercharger. In other examples, both the first boosting device and the second boosting device may be electric superchargers or electric turbochargers.

[0022] In the depicted example, the electric supercharger 13 includes a first compressor 110 driven by an electric motor 108. Specifically, the fan of the first compressor 110 can be driven along the supercharger compressor shaft 80 by the power received from the electric motor 108. In some examples, the first compressor 110 of the supercharger 13 can be additionally driven by the engine crankshaft via a clutch and gear mechanism. The electric motor 108 can be powered by an onboard energy storage device (such as a system battery 45). The electric motor 108 can be powered by an alternator 46 in addition or alternatively. The amount of power delivered to the electric motor 108 can be varied in order to adjust the duty cycle of the supercharger. In one example, the amount of power delivered to the electric motor 108 can be increased to increase the speed of the first compressor 110, wherein the power load imposed on the alternator is correspondingly increased and the alternator current is correspondingly reduced. Due to the electric assistance, the supercharger 13 can quickly speed up the rotation, thereby providing a fast-acting or high-frequency boost actuation.

[0023] During selected conditions, air may enter the first compressor 110 when the opening of the electric supercharger bypass valve (ESBV) 72 is reduced, thereby directing intake air from the air box 112 through the first compressor bypass passage 70 and the first compressor 110, where the air is pressurized for delivery to the second compressor 114. Fresh air received at the inlet of the second compressor 114 is then compressed and directed into the engine 10. As the opening of the ESBV 72 increases, the amount of air that enters the second compressor 114 without passing through the first compressor bypass passage 70 and the first compressor 110 increases. In the fully open condition of the ESBV 72, compressed air may be delivered to the engine 10 only via the second compressor 114 of the turbocharger 15. By spinning up the electric supercharger via the electric motor, a burst of boost pressure may be quickly provided to the engine.

[0024] The electric motor 108 may be configured as a motor generator. Thus, during conditions where electric assistance is needed for boost buildup, the electric motor may provide positive torque to drive the centrifugal compressor of the supercharger (or turbocharger shaft) to improve transient boost pressure delivery. However, the electric motor is also capable of energy recovery by "braking" the motor shaft. Therein, negative torque may be applied to the compressor (or shaft), thereby reducing compressor speed and simultaneously charging a system battery (such as battery 45) coupled to the motor. As described in reference Figure 2 As stated, the engine controller may control the timing and amount of positive and negative torque applied from the electric motor to the supercharger in order to regulate throttle inlet pressure (TIP) / boost pressure.

[0025] The turbocharger 15 includes a second compressor 114 driven by a turbine 116. The second compressor 114 is shown as a turbocharger compressor mechanically coupled to the turbine 116 via a shaft 19, and the turbine 116 is driven by the expanding engine exhaust. In one embodiment, the turbocharger may be a twin scroll device. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), in which the turbine geometry is actively varied according to engine operating conditions.

[0026] Fresh air is directed into engine 10 along intake passage 42 via air box 112 and flows to second compressor 114. During selected conditions, as explained below, air compressed by turbocharger 15 may be recirculated from the outlet of second compressor 114 to the inlet of second compressor 114 via second compressor bypass passage 60 by adjusting the opening of compressor recirculation valve (CRV) 62. CRV 62 may be a continuously variable valve, and increasing the opening of CRV 62 may include actuating (or energizing) a solenoid of the valve.

[0027] One or both of the CRV 62 and the ESBV 72 may be continuously variable valves, wherein the position of the valve is continuously variable from a fully closed position to a fully open position. Alternatively, the CRV 62 may be a continuously variable valve, while the ESBV 72 is a switch valve. In certain embodiments, the CRV 62 may be partially opened during boost engine operation to provide surge margin. Here, the partially open position may be a default valve position. Then, in response to an indication of surge, the opening of the CRV 62 may be increased. For example, the CRV 62 may be adjusted from a default, partially open position toward a fully open position, wherein the degree of opening is based on a surge indication (e.g., compressor ratio, compressor flow rate, pressure difference across the compressor, etc.). In an alternative example, the CRV 62 may remain closed during boost engine operation (e.g., peak performance conditions) to reduce boost response time and increase peak performance.

[0028] The second compressor 114 is coupled to a throttle valve 20 via a charge air cooler (CAC) 18 (also referred to herein as an intercooler). Air flows from the second compressor 114 through the CAC 18 and the throttle valve 20 to the intake manifold 22. The CAC 18 may be, for example, an air-to-air heat exchanger or a water-to-air heat exchanger. The intake manifold pressure (e.g., the pressure of the charge air within the intake manifold) may be determined using a manifold absolute pressure (MAP) sensor 124.

[0029] The intake manifold 22 is coupled to a series of combustion chambers 30 through a series of intake valves (not shown). The combustion chambers are further coupled to an exhaust manifold 36 via a series of exhaust valves (not shown). In the illustrated embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include multiple exhaust manifold segments. A configuration with multiple exhaust manifold segments may enable the outflow from different combustion chambers to be directed to different locations in the engine system.

[0030] In one embodiment, each of the exhaust valve and the intake valve may be electronically actuated or electronically controlled. In another embodiment, each of the exhaust valve and the intake valve may be cam actuated or cam controlled. Whether electronically actuated or cam actuated, the timing of the opening and closing of the exhaust valve and the intake valve may be adjusted to achieve desired combustion performance and emission control performance. For example, the cam timing may be adjusted via a variable cam timing system to move the intake cam and the exhaust cam to a position that provides the best volumetric efficiency for a given operating condition.

[0031] One or more fuels such as gasoline, an alcohol fuel blend, diesel, biodiesel, compressed natural gas, etc. may be supplied to combustion chamber 30. Fuel may be supplied to combustion chamber 30 via direct injection, port injection, throttle body injection, or any combination thereof. In the depicted example, fuel is provided to each combustion chamber 30 via direct injection via fuel injector 66 (and Figure 1 Only one fuel injector is shown, with each combustion chamber including a fuel injector coupled thereto). Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. Combustion may be initiated in the combustion chamber via spark ignition and / or compression ignition.

[0032] like Figure 1 As shown, exhaust gas from exhaust manifold 36 is directed to turbine 116 to drive the turbine. When reduced turbine torque is desired, a portion of the exhaust gas may instead be directed through wastegate 90, thereby bypassing the turbine. Wastegate actuator 92 (e.g., wastegate valve) may be actuated open to release at least some exhaust pressure from upstream of turbine 116 to a location downstream of turbine 116 via wastegate 90. By reducing exhaust pressure upstream of turbine 116, turbine speed may be reduced.

[0033] The combined flow from turbine 116 and wastegate 90 flows through emission control device 170. Generally, emission control device 170 may include one or more exhaust aftertreatment components configured to reduce the amount of one or more substances in the exhaust flow. For example, one exhaust aftertreatment component may be configured to capture NO from the exhaust flow when the exhaust flow is lean. x and reduces captured NOx when the exhaust stream is enriched x In other examples, the exhaust aftertreatment component may be configured tox Disproportionate or selective reduction of NO with the aid of a reducing agent x In other examples, emission control device 170 includes a three-way catalyst configured to oxidize residual hydrocarbons and carbon monoxide while reducing NO in the exhaust flow. x Different exhaust aftertreatment catalysts having any such functionality may be arranged alone or together in the washcoat or elsewhere in emission control device 170. In certain embodiments, emission control device 170 may further include a regenerable soot filter configured to capture and oxidize soot particles in the exhaust flow.

[0034] All or a portion of the treated exhaust gas from emission control device 170 may be released to the atmosphere via exhaust conduit 35. However, depending on operating conditions, some exhaust gas may instead be diverted to intake passage 42 via an exhaust gas recirculation (EGR) passage (not shown) including an EGR cooler and an EGR valve. The EGR may be recirculated to the inlet of first compressor 110, the inlet of second compressor 114, or both.

[0035] One or more sensors may be coupled to the inlet of the second compressor 114 (as shown) and / or the inlet of the first compressor 110 (not shown). For example, a temperature sensor 55 may be coupled to the inlet of the second compressor 114 for estimating the compressor inlet temperature. As another example, a pressure sensor 56 may be coupled to the inlet of the second compressor 114 for estimating the air pressure entering the second compressor. The pressure upstream of the second compressor 114 and downstream of the first compressor 110 as measured by the pressure sensor 56 will be referred to as P1 in this article. Still other sensors may include, for example, an air-fuel ratio sensor, a humidity sensor, etc. In other examples, one or more of the conditions of the second compressor inlet (such as humidity, temperature, etc.) may be inferred based on the engine operating conditions. The sensor may estimate the condition of the intake air received from the intake passage at the inlet of the second compressor and the charge recirculated from the upstream of the CAC18. One or more sensors may also be coupled to the intake passage 42 upstream of the first compressor 110 for determining the composition and condition of the charge entering the compressor. These sensors may include, for example, a pressure sensor 58. The pressure upstream of the air box 112 (e.g., atmospheric pressure) as measured by pressure sensor 58 will be referred to herein as P0. Additionally, a throttle inlet pressure (TIP) sensor 59 may be coupled downstream of the CAC 18 and upstream of the throttle valve 20 for use in estimating the boost pressure delivered to the engine. The pressure downstream of the CAC 18 and upstream of the throttle valve 20 as measured by the TIP sensor 59 will be referred to herein as P2. The overall pressure ratio across the compound boost system is defined as The pressure ratio across the first compressor 110 is defined as And the pressure ratio across the second compressor 114 is defined as

[0036] During an operator tip-in event, turbo lag can occur when switching from engine operation without boost to engine operation with boost in response to an increase in operator torque demand. This is due to the delay in spinning up the turbine 116 due to the turbocharger being a slower acting compression device, and the brief reduction in flow through the second compressor 114 when the throttle valve 20 opens at a tip-in. The same situation occurs when the engine is operating with boost, and there is a transient increase in boost demand due to the increased application of the accelerator pedal by the vehicle operator. In order to reduce this turbo lag, both the supercharger 13 and the turbocharger 15 can be enabled during those selected conditions. In particular, a faster acting electrically actuated compression device (electric supercharger) can be used to improve transient boost response. Specifically, in response to a tip-in, the wastegate actuator 92 can be closed (e.g., fully closed) to increase exhaust flow through the turbine 116. When the turbine 116 spins up, boost pressure can be provided momentarily by the first compressor 110. Activating the supercharger 13 may include drawing energy from the system battery 45 to spin the electric motor 108 and thereby speed up the first compressor 110. In addition, the ESBV 72 may be closed (e.g., fully closed) so that a larger portion of the intake air flows through the bypass passage 70 and is compressed by the first compressor 10. In addition, the CRV 62 may be closed (e.g., fully closed) so as to increase the flow through the second compressor 114. When the turbine has been sufficiently spun up and the turbocharger is able to provide the desired amount of boost, the first compressor 110 may be decelerated by disabling the electric motor 108 (e.g., by interrupting the power supply from the battery 45 to the electric motor 108). In addition, the ESBV 72 may be opened so that a larger portion of the air can bypass the first compressor 110. As further described herein, activation (and deactivation) of the first compressor 110 may be precisely controlled to provide a desired boost pressure while reducing overshoot or undershoot of the desired boost pressure, minimizing boost pressure disturbances when the first compressor 110 is enabled / disabled, and minimizing the duration of operation of the first compressor 110, thereby minimizing the amount of power consumed by the supercharger 13. As described in reference Figures 2 to 6As described, the desired amount of boost can be provided by dynamically coordinating the turbocharger 15 and the supercharger 13 based on the boost capacity of the turbocharger 15 at a given time (e.g., the pressure ratio across the second compressor 114) and the desired total boost pressure ratio. The controller can dynamically adjust the pressure ratio distribution to the supercharger based on the lack of air flow incurred at the turbocharger. In addition, the controller can adjust the timing and output of the motor torque supplied by the electric motor to the supercharger to reduce pressure overshoot while maximizing energy recovery.

[0037] During an operator tip-out event, when switching from engine operation with boost to engine operation without boost (or reduced boost), compressor surge may occur. This is due to the reduced flow through the second compressor 114 when the throttle valve 20 is closed at the tip-out. The reduced forward flow through the second compressor can cause surge and degrade the performance of the turbocharger. In addition, surge can cause noise, vibration and discomfort (NVH) issues, such as undesirable noise from the engine intake system. In order to enable the torque demand to be quickly reduced in response to the tip-out during the default mode of vehicle operation without incurring compressor surge, at least a portion of the charge compressed by the second compressor 114 can be recirculated to the compressor inlet. This allows the excess boost pressure to be substantially relieved immediately. In particular, the CRV 62 can be opened to recirculate (warm) compressed air from the outlet of the second compressor 114 upstream of the CAC 18 to the inlet of the second compressor 114. In certain embodiments, the compressor recirculation system may additionally or alternatively include a recirculation passage for recirculating cooled compressed air from downstream of the CAC 18 to the inlet of the second compressor 114. Additionally, the wastegate actuator 92 may be moved to a more open (e.g., fully open) position such that more exhaust flow travels to the tailpipe while bypassing the turbine, thereby accelerating the rotational slowing of the turbine.

[0038] The controller 12 may be included in the control system 14. The controller 12 shown receives information from a plurality of sensors 16 (various examples of which are described herein) and sends control signals to a plurality of actuators 81 (various examples of which are described herein). As an example, the sensors 16 may include an exhaust gas sensor 126 located upstream of the turbine 116, a MAP sensor 124, an exhaust gas temperature sensor 128, an exhaust gas pressure sensor 129, a compressor inlet temperature sensor 55, a compressor inlet pressure sensor 56 (e.g., for measuring P1), a mass air flow (MAF) sensor 57, a pressure sensor 58 (e.g., for measuring P0), and a TIP sensor 59 (e.g., for measuring P2). Other sensors, such as additional pressure sensors, temperature sensors, air / fuel ratio sensors, and composition sensors, may be coupled to various locations in the engine system 100. The actuators 81 may include, for example, the throttle valve 20, the CRV 62, the ESBV 72, the electric motor 108, the wastegate actuator 92, and the fuel injector 66. The controller 12 may receive input data from various sensors, process the input data, and employ various actuators to adjust engine operation based on the signals received and instructions stored in the memory of the controller. Figure 2 (and Figure 6 ), the controller may employ actuators in response to processed input data. As an example, in response to measured pressure indicating a boost pressure deficiency when operating a turbocharger, the controller may actuate an electric motor driving a supercharger compressor and actuate a closed ESBV to provide additional boost via the supercharger compressor.

[0039] In this way, Figure 1The components enable a vehicle system to include: an engine having an intake; an accelerator pedal for receiving an operator torque demand; a compound boost system including: a first (auxiliary) supercharger compressor driven by an electric motor receiving power from a battery, and a second (primary) turbocharger compressor driven by an exhaust turbine, the second compressor positioned downstream of the first compressor in the engine intake; a bypass including a bypass valve coupled across the first compressor; a wastegate including a wastegate actuator coupled across the exhaust turbine; a first pressure sensor coupled to the intake upstream of the first compressor to estimate atmospheric a pressure sensor coupled to an intake device downstream of the first compressor and upstream of the second compressor for estimating a turbocharger inlet pressure; a third pressure sensor coupled to the intake device downstream of the second compressor for estimating a throttle inlet pressure; and a controller having computer readable instructions stored on a non-transitory memory for: commanding a total pressure ratio across the compound boost system via adjustment of a wastegate actuator in response to an operator torque demand; and varying the commanded pressure ratio across the first compressor via adjustment of an output of the electric motor based on an air flow deficit at the second compressor, the air flow deficit estimated based on an actual pressure ratio across the second compressor. In one example, commanding the total pressure ratio may include: decreasing an opening of the wastegate actuator to increase the actual pressure ratio across the second compressor as the operator torque demand increases, and wherein varying the commanded pressure ratio across the first compressor includes: operating the electric motor in a motoring mode when the air flow deficit increases above a threshold, and operating the electric motor in a generating mode when the air flow deficit decreases below the threshold. In another example, the controller may include further instructions for closing the ESBV to increase the pressure ratio across the first compressor when the air flow deficit increases above a threshold, and opening the ESBV to decrease the pressure ratio across the first compressor when the air flow deficit decreases below the threshold.

[0040] Figure 1The components may further enable the controller to command a total pressure ratio of a first compression device of the engine intake device based on an operator torque demand; provide a positive motor torque to increase the pressure ratio of the first compressor when the actual pressure ratio of the second compressor is away from the total pressure ratio; and provide a negative motor torque to reduce the pressure ratio of the first compressor when the actual pressure ratio of the second compressor is close to the total pressure ratio. In the foregoing example, commanding the total pressure ratio may include: reducing the opening of the wastegate actuator to increase the actual pressure ratio across the second compressor as the operator torque demand increases, wherein providing the positive motor torque includes operating the electric motor at a motor output in a motor operating mode based on an air flow deficit, the air flow deficit being estimated based on a difference between the actual pressure ratio of the second compressor and the total pressure ratio, and wherein providing the negative torque includes operating the electric motor at a generator output in a generator mode based on the difference. In a further example, the controller may further include instructions for: closing the ESBV while providing the positive motor torque or the negative motor torque. The system may further include a first pressure sensor connected to the intake device upstream of the first compressor to estimate atmospheric pressure; a second pressure sensor connected to the intake device downstream of the first compressor and upstream of the second compressor to estimate a turbocharger inlet pressure; and a third pressure sensor connected to the intake device downstream of the second compressor to estimate a throttle inlet pressure; wherein the controller may further include instructions for: estimating a total pressure ratio based on an output of the third pressure sensor relative to an output of the first pressure sensor; estimating an actual pressure ratio across the second compressor based on an output of the third pressure sensor relative to an output of the second pressure sensor; and estimating an actual pressure ratio across the first compressor based on an output of the second pressure sensor relative to an output of the first pressure sensor.

[0041] Now go to Figure 2 , which shows an example method 200 for operating a compound boost engine system having a staged boost device. The compound boost engine system may include at least two intake air compression devices arranged in series, at least one of which includes electric assistance. One of the at least two compression devices may be a slower acting (lower frequency) compression device, such as a turbocharger configured as a primary boost device, and the other of the two compression devices may be a faster acting (higher frequency) compression device, such as an electric mechanical supercharger configured as an auxiliary boost device. Instructions for performing method 200 and the remaining methods included herein may be issued by a controller (e.g., Figure 1 The controller 12) is based on instructions stored in the memory of the controller and in conjunction with sensors from the engine system (such as those referenced above). Figure 1 The controller may use an engine actuator of the engine system, such as an electric supercharger bypass valve (e.g., Figure 1 ESBV72), electric motors (such as Figure 1 108), and a turbocharger wastegate actuator (e.g., Figure 1 of the wastegate actuator 92) to regulate engine operation according to the method described below.

[0042] At 202, method 200 includes estimating and / or measuring engine operating conditions. For example, the evaluated operating conditions may include engine speed, pedal position, operator torque demand, manifold absolute pressure, manifold air flow, manifold air temperature, ambient conditions (such as ambient temperature, barometric pressure and humidity), engine coolant temperature, etc. For example, barometric pressure may be measured by a pressure sensor such as Figure 1 The pressure sensor 58 measures.

[0043] At 204, method 200 includes determining whether a boost is requested. In one example, a boost may be requested at medium to high engine loads. In another example, a boost may be requested in response to an operator pressing an accelerator pedal or an increase in driver torque demand. If a boost is not requested, such as when the engine load is low or the driver torque demand is low, method 200 proceeds to 206 and includes operating the engine with natural aspiration (e.g., manifold vacuum). Operating the engine with natural aspiration may include not activating a stepped boost device. For example, an electric motor (e.g., electric motor 108) used to drive an electric mechanical supercharger may not be powered, and a turbocharger wastegate actuator may be commanded to be fully open in order to direct a portion of the exhaust gas to bypass a turbine of the turbocharger (e.g., Figure 1 After 206, method 200 ends.

[0044] If boost is requested at 204, such as in response to a tip-in event, method 200 proceeds to 208 and includes generating a total pressure ratio command for the slower primary compression device based on the operator torque / boost request. Here the total pressure ratio is a steady-state desired pressure ratio commanded by and achieved by the primary compression device over time. The commanded total pressure ratio may be defined as in represents the desired throttle inlet pressure or the desired pressure at the outlet of the compound boost system. In one example, this is the pressure at the outlet of the slower acting primary compression device, such as the outlet pressure of a turbocharger compressor. P0 represents the inlet pressure of the compound boost system or atmospheric pressure. In one example, this is the pressure at the inlet of the faster acting auxiliary compression device, such as the inlet pressure of an electric supercharger compressor. In a configuration where the auxiliary compression device is staged upstream of the primary compression device, the actual outlet pressure P2 of the primary compression device (e.g., as measured by a TIP sensor) may be described as:

[0045]

[0046] Where P1 is the outlet pressure of the auxiliary compression device, which is also the inlet pressure of the main compression device. P2 also corresponds to the total boost pressure achieved at both ends of the step-up boost device. As can be seen from the above equation, is the pressure ratio across the auxiliary compression device, and is the pressure ratio across the main compression device. In other words, the total pressure ratio across the system is the product of the pressure ratios across each compressor in series. The pressure ratio represents the capacity of the boost device (such as an electric mechanical supercharger, turbocharger, or compound boost system). However, the throttle inlet pressure cannot separate the boost contribution from each device. Therefore, by coordinating the pressure ratio commanded to each boost device and the steady-state desired pressure ratio P2 * / P0 can improve the transient boost response.

[0047] In one example, the controller may generate a total pressure ratio command by estimating P0 based on the output of the air pressure sensor. The controller may further estimate P0 based on the output of the operator accelerator pedal position sensor. The controller may reference a lookup table where the target boost pressure is stored as a function of pedal position, such as increasing the target boost pressure as accelerator pedal depression increases (increases as the pedal position moves toward the fully depressed position). Alternatively, the controller may use a model or algorithm that uses pedal position as an input and provides a target boost pressure as an output. The pressure ratio command may then be determined as P2 * / P0.

[0048] In one example, the turbocharger may be controlled to deliver the full requested boost pressure Therefore, the overall pressure ratio of the commanded turbocharger compressor can be determined as:

[0049]

[0050] Where t represents time.

[0051] At 210, the method includes adjusting a boost pressure actuator of a slower-acting primary compression device based on the generated total pressure ratio command. For example, where the primary compression device is a turbocharger, the controller may generate a command for a wastegate coupled across an exhaust turbine based on the generated total pressure ratio command. The command for the wastegate may indicate a degree of opening of a wastegate valve sent to a wastegate actuator. In one example, as the total pressure ratio command increases, the commanded degree of opening of the wastegate may decrease. For example, at a command above a threshold pressure ratio, the wastegate may be fully closed.

[0052] In one example, the controller may input the total pressure ratio command and MAF (as determined from the intake MAF sensor) into a lookup table (or model or algorithm) that outputs the position of the turbocharger wastegate actuator that corresponds to the turbine speed and the corresponding turbocharger compressor speed. In another example, the controller may reference a compressor map to determine the desired turbocharger compressor speed for the commanded total boost pressure ratio and given air flow conditions, and may further correlate the resulting turbocharger compressor speed with the corresponding position of the turbocharger wastegate actuator. Further, the actual turbocharger pressure ratio Can be used as feedback for wastegate control. For example, as the actual turbocharger pressure ratio increases, the turbocharger wastegate actuator can be adjusted to a more open position. Additionally or alternatively, if the turbocharger is within a threshold range of surge, the opening of one or both of the CRV and the wastegate actuator can be increased.

[0053] It should be appreciated that in further examples, the commanded total pressure ratio may be adjusted (e.g., limited) to account for any mechanical constraints of the boost engine system, such as a temperature constraint, a pressure constraint, or a speed constraint of the primary compression device, above which the performance of the primary compression device may be adversely affected, such as due to hardware issues. In one example, if the commanded total pressure ratio based solely on the operator torque demand is predicted to result in a compressor inlet temperature (of the primary compression device) or a compressor outlet temperature above a threshold temperature for hardware degradation of the primary compression device, the controller may reduce the commanded total pressure ratio by a factor based on the difference between the predicted temperature and the threshold temperature.

[0054] Due to the slow response time of the primary compression device (here, the turbocharger), there may be a temporary lack of boost pressure. For example, the lack may be due to the steady-state boost pressure delivery requiring the turbine to spin up before it can drive the turbocharger compressor. At 212, the method includes estimating the lack of boost pressure and the corresponding air flow deficiency at the primary compression device. For example, the turbocharger boost pressure ratio lack (Π * ) can be defined as follows:

[0055]

[0056] The controller may calculate a boost pressure deficit as a function (e.g., a ratio or difference) of an actual pressure ratio across the primary compression device relative to a desired or commanded pressure ratio. The actual pressure ratio may be determined as the compressor inlet pressure of the primary compression device relative to the actual throttle inlet pressure. This boost pressure deficit reflects insufficient air flow at the primary compression device and is used to distribute a pressure ratio command to the auxiliary compression device.

[0057] For example, where the auxiliary compression device is an electric supercharger, the pressure ratio commanded to the electric supercharger is dynamically scheduled based on the turbocharger's capabilities (as inferred from the turbocharger's actual pressure ratio P2 / P1). This allows the controller to accurately know in real time the exact boost pressure deficit as the turbine spins up, and regulate the electric supercharger speed command (n_eSC) to reduce the deficit. Additionally, the controller is able to form closed-loop system dynamics by knowing the electric supercharger's pressure ratio (P1 / P0), as described herein.

[0058] For example, the desired pressure ratio target of an electric supercharger is defined as * , where there is a constraint on the turbocharger pressure ratio as follows:

[0059]

[0060] If P1 > P2 , this constraint is included to prevent the desired pressure ratio target for the electric supercharger from exceeding the total desired system pressure ratio, which may occur briefly after throttle opening.

[0061] At 214, the method includes generating a pressure ratio command for the faster auxiliary compression device. In one example, the pressure ratio command is generated based on a pressure ratio deficiency. In another example, the pressure ratio command is generated based on a corresponding air flow deficiency. For example, the controller may estimate the inlet pressure of the electric mechanical supercharger (e.g., based on a measured atmospheric pressure) and use a lookup table, model, or algorithm to calculate a desired outlet pressure of the electric mechanical supercharger that satisfies the air flow deficiency. The pressure ratio command for the electric mechanical supercharger may then be determined as a ratio of the actual inlet pressure relative to the desired outlet pressure.

[0062] At 216, the method includes commanding electric assistance to the auxiliary compression device. In particular, the controller may command a positive motor torque from the electric motor to the auxiliary compression device (such as an electric supercharger) based on a pressure ratio command based on the lack. In one example, commanding the positive motor torque includes estimating a compressor speed of the electric compressor, such as via a lookup table, a map, or an algorithm, that will provide a desired compressor outlet pressure at the electric supercharger, and then estimating a motor speed (or degree of electric assistance) of the electric motor that will provide an estimated compressor speed. The controller may then adjust the duty cycle commanded to the electric motor so as to operate the motor at the desired motor speed.

[0063] Next, at 218, the actual boost pressure may be compared relative to the target throttle inlet pressure to determine whether the actual boost pressure is within a threshold of the target throttle inlet pressure (TIP). For example, it may be determined whether the outlet pressure of the turbocharger is within a threshold of the desired TIP, such as when the difference between the outlet pressure and the desired TIP is less than a threshold. In an alternative example, the ratio of the outlet pressure of the turbocharger may be compared to the target throttle inlet pressure. If the difference (or ratio) is not within the threshold, at 220, the controller continues to dynamically adjust the distribution of the pressure ratios at both ends of the main compression device and the auxiliary compression device. In particular, as the turbine spins faster and the boost capacity of the turbocharger increases, the pressure ratio at both ends of the turbocharger may begin to approach the commanded pressure ratio, the deficit may begin to decline, and therefore the pressure ratio (and electric assistance) commanded at the electric supercharger may be reduced.

[0064] In this way, the controller continuously adjusts the auxiliary compression device in real time based on the actual capacity of the primary compression device. The controller may use a dynamic allocation module, as described herein. Figure 5 , to adjust the pressure ratio as further described herein. Thus, as the slower responding turbocharger accelerates, the desired assistance from the faster responding electric mechanical supercharger gradually ceases. Eventually, when the turbocharger is able to maintain the total desired boost, no assistance from the electric mechanical supercharger is required. Figure 3 An example of a dynamic distribution of pressure ratios with minimal reliance on electric assistance and the resulting accelerated achievement of a target boost pressure is described.

[0065] Briefly go to Figure 3 , map 300 depicts pressure ratio across the y-axis and time along the x-axis. The total commanded pressure ratio based on the torque demand, represented by P*2 / P0, is depicted by dashed line 302. As such, this is the pressure ratio commanded to the primary compression device. The actual pressure ratio of the primary compression device, represented by P2 / P1, is depicted by dashed line 304 and represents the boost capability of the primary compression device. Over time, this will change and develop to a gradually commanded steady state value due to the slower response time of the primary compression device. * A temporary pressure ratio deficit (unclipped) is depicted by dashed line 306. A clipped version of this pressure ratio deficit is used to schedule a pressure ratio commanded to the auxiliary compression device, which has a faster response time. The pressure ratio commanded to the auxiliary compression device, represented by P*1 / P0, is depicted by solid line 308.

[0066] In response to the torque demand, a total pressure ratio command 302 is determined and commanded to the main compression device. However, due to the slower response time of the main compression device (e.g., turbo lag), the actual pressure ratio 304 achieved at the main compression device is low, and the initial pressure ratio deficiency 306 may be significant. If this pressure ratio deficiency is not resolved, the transient boost response will be adversely affected. The pressure ratio deficiency is satisfied by commanding a pressure ratio 308 to the auxiliary compression device. In particular, during the initial portion of the boost response, a larger portion of the total pressure ratio is dynamically allocated to the auxiliary compression device due to the larger pressure ratio deficiency incurred at the main compression device. Then, as the main compression device rotates faster, a larger portion of the total pressure ratio is delivered by the main compression device, and the contribution of the auxiliary compression device is dynamically reduced by ceasing to command pressure force to the auxiliary compression device. Therefore, the overall reliance on electric assistance is minimized while improving the transient boost response.

[0067] Back to Figure 2 , at 218, if the boost pressure is within a threshold of the target TIP, but still below the target TIP, then at 222, the method includes providing a negative motor torque from the electric motor to the auxiliary compression device. This allows the boost pressure to coast to the target TIP, thereby reducing the possibility of pressure overshoot. In addition, the electric assistance from the motor is reduced earlier, thereby improving fuel economy. In addition, by operating the motor as a generator in the area where pressure overshoot may occur, energy recovery via the motor is achieved, thereby further improving fuel economy while also improving boost response. The controller may use a lead compensator module, such as described herein in Figure 5 As further described herein, the timing of discontinuing electric assistance from the motor (e.g., related to turbine speed or boost pressure) and when the motor transitions to operating as a generator may be determined. In one example, the motor may rotate as a generator at a speed based on the predicted overshoot. The routine then ends.

[0068] As mentioned before, the compound boost system can be described as:

[0069]

[0070] Wherein P0 is the inlet pressure of the first boosting device, and P1, P2 are the outlet pressures (TIP) from the first boosting device and the second boosting device. Refers to the desired pressure target of the first boost device and the second boost device. In the above configuration, the first boost device is a transient (auxiliary) device, such as an electric mechanical supercharger, and the second boost device is a primary device, such as a turbocharger. The control reference of the first boost device is determined as:

[0071]

[0072] If P1>P2, clipping is included to prevent the desired pressure target of the first boost device from overtaking the desired pressure target of the second boost device, which may occur briefly after the throttle is opened. The primary boost device is required to deliver the entire desired boost pressure. Therefore, the target of the second device is The full pressure ratio (from ambient) is always available. In this case:

[0073]

[0074] In this way, the base station controller can be rewritten to not operate the auxiliary boost device or to operate the auxiliary boost device in a continuous manner, and vice versa for the main boost device.

[0075] If the controller is conservatively calibrated to minimize P2 overshoot, the boost pressure response can become slower than the maximum system capability. Therefore, by using a lead compensator along with aggressive calibration of the controller, the transient response of the boost system is improved. At the same time, as P2 approaches Previously, the lead compensator would have requested a speed reduction. This command enables the electric motor's energy recovery mode, thus maximizing the window for energy recovery.

[0076] The lead compensator in the Laplace domain can be expressed as:

[0077]

[0078] Input U is the pressure ratio error of the electric supercharger:

[0079]

[0080] For implementation in a discrete system, the following transformation is derived:

[0081] x k =(1-f)x k-1 +fu k ,

[0082] y k =(1-r)x k +ru k ,

[0083] Where f is the time constant in the discrete domain, r is the lead ratio, T s For the execution rate.

[0084] The output of the lead compensator is clipped to allow the range of the lead effect on U to be regulated in either the increasing or decreasing direction.

[0085]

[0086] Reference here Figure 4 An example of lead compensation of the pressure ratio at an electric supercharger and the resulting reduction of pressure overshoot and accelerated activation of energy recovery at an electric motor is described.

[0087] Briefly go to Figure 4 , map 400 depicts how lead compensation and dynamic pressure ratio distribution are used to improve transient boost response while maximizing energy recovery opportunities. Map 400 includes map 402 and map 404. Map 404 depicts the change in electric assistance commanded to the electric supercharger (across the y-axis) over time (along the x-axis) relative to the distribution of pressure ratios (across the y-axis) between the turbocharger and the electric supercharger in the same time frame (along the x-axis), as shown in map 402. The change in electric assistance commanded to the electric supercharger (across the y-axis) is depicted by solid line 408. * 4. The total command pressure ratio based on the torque demand represented by P2 / P0. Thus, this is the pressure ratio commanded to the main compression device, here the turbocharger. The actual pressure ratio achieved via the compound boost system without lead compensation (w / o LC) represented by P2 / P0 is depicted by curve 410, and is compared with P2 / P0 achieved with lead compensation (with LC) depicted by curve 412. The motor speed commanded to the electric mechanical supercharger without lead compensation (w / o LC) is shown at curve 430, and is compared with the motor speed command with lead compensation (with LC) depicted by curve 434. A portion of the motor speed command received via the lead compensator module of the controller is shown at curve 432.

[0088] Before t1, the engine is operated without boost, and therefore the commanded pressure ratio is low. At t1, in response to an increase in the operator torque demand, the boost pressure needs to increase. Therefore, the total pressure ratio command (408) generated based on the torque demand increases. This is a signal commanded to the turbocharger for steady-state realization of the target TIP. However, due to the slow response time of the turbocharger, there is a temporary pressure ratio shortage that is satisfied by actuating the electric supercharger and dynamically allocating a larger portion of the total commanded pressure ratio of the electric supercharger. In particular, at t1, the pressure ratio command is delivered to the electric supercharger (e.g., based on the corresponding lack of air flow) as a function of the boost pressure, which is caused by the slow response of the turbocharger. Therefore, the motor speed of the electric supercharger increases (430, 434), which results in an increase in the pressure ratio across the supercharger. At this point, the electric motor operates in motor mode to provide energy to the supercharger.

[0089] As the turbine spins up faster, it can account for a larger portion of the total pressure ratio command. After t2, when the pressure ratio at the turbocharger is within a threshold of the total pressure ratio but still below the total pressure ratio, the lead compensator module sends a signal (432) to the electric motor to reduce the motor speed and provide negative motor torque. At this time, the electric motor operates in a generating mode to recover energy from the supercharger. Due to the timing of the lead compensation before the target total pressure ratio is reached, the pressure ratio at the turbocharger (412) coasts to the target pressure ratio. If lead compensation is not provided, the pressure ratio at the turbocharger (410) will exceed the total pressure ratio (i.e., P2 / P0 will exceed P2 * / P0), resulting in a torque error. This can affect drivability. In addition, due to the timing of the lead compensation before the target total pressure ratio is reached, the pressure ratio at the supercharger is reduced in a timely manner. If no lead compensation is provided, the pressure ratio at the supercharger (420) will also exceed the commanded pressure ratio (i.e., P1 / P0 will exceed P1 * / P0). Not only will this result in a reduction in fuel economy due to the electric supercharger operating longer than necessary, but an additional reduction in fuel economy will occur due to missed energy recovery opportunities. Conversely, by providing lead compensation earlier, the pressure overshoot is resolved by absorbing torque at the motor. As a result, the overall transient response of the boosted engine is improved while also extending the energy recovery window of the electric motor.

[0090] It should be understood that the electric supercharger may be a transient device that is not continuously controlled. The supervisory controller may coordinate the operation of the electric supercharger and the electric supercharger bypass valve. The primary purpose of the supervisory controller may be to determine when to activate and deactivate the electric supercharger and the electric supercharger bypass valve to meet control needs based on system constraints and hardware protections. At a high level, when activation criteria are met and no system faults are observed, the electric supercharger is activated and the bypass valve is closed. Once deactivation criteria are met or a system fault is observed, the electric supercharger is deactivated and the bypass valve is opened.

[0091] There may be several considerations in the design of the activation strategy. First, the controller may activate the electric supercharger only when necessary, such as when the vehicle drivability is unacceptable due to the slow response of the turbocharger. Second, it may be desirable to take proactive action if the strategy does not have to wait until unacceptable drivability is observed. Finally, the controller aims to reduce unnecessary activations in the event of a driver changing his mind.

[0092] Due to the lack of boost pressure ratio (Π * ) can be used as an indicator to determine the lack of driver demand (which represents driving performance), so it can be determined by looking at Π *The rate of change of is used to achieve active action, and the threshold value (f2) for initiation is determined as Π * The function is as follows:

[0093]

[0094] In Π * and Add two first-order low-pass filters (H lp ) to mitigate "false positive" activations during driver change of mind events (such as when the driver actively presses the accelerator pedal but quickly removes the command), as follows:

[0095]

[0096]

[0097] where h 1,2 are two time constants in the discrete domain.

[0098] via Figure 7 The sample acceleration trajectory at 700 shows the launch strategy. The trajectory shown at the map 700 is constructed as follows: wherein the X-axis depicts the filtered boost pressure deficiency and the Y-axis depicts the filtered rate of change of the boost pressure deficiency. The launch threshold depicted by the solid line 702 is determined as the filtered Π * The acceleration trajectory when no electric assistance from the electric motor is required is shown by the empty circle 706. The acceleration trajectory when electric assistance from the electric motor is required is shown by the solid circle 704. The calibration shows that at * When the rate of change is high, even if the absolute value Π * On the other hand, if Π * If the pressure builds up to an unacceptable level, the strategy will activate the electric supercharger. The primary criteria for deactivating the electric supercharger are when the turbocharger is able to maintain the desired boost pressure, or when the boost pressure lacks a reduction and falls below a threshold, such as in the following situations:

[0099] Π * ≤α

[0100] Where α is a calibrable constant.

[0101] It should be understood that while the examples discussed above relate to configurations including a turbocharger coupled to an electric supercharger, this is not meant to be limiting. In other examples, the turbocharger may be configured with electric assistance (e.g., as an electric turbine having an electric motor coupled to a compressor, turbine, or turbocharger shaft). Further examples may relate to a boosted engine having a staged supercharger or a staged turbocharger, at least one of which has electric assistance.

[0102] Now go to Figure 5 , which shows a block diagram of an example control architecture for a compound boost system having a higher frequency compression device with electric assistance and a lower frequency compression device. For example, the control architecture may be applied to a system having an electric supercharger compressor (e.g., Figure 1 The first compressor 110 of the engine system is coupled to the turbocharger compressor (eg, Figure 1 The control architecture may be provided by a controller (e.g., Figure 1 The controller 12) uses and executes the control method (such as Figure 2 Method 200) to regulate boost pressure delivery.

[0103] An electric supercharger controller (C1) includes: a dynamic distributor (D1) that apportions a desired boost pressure control reference; a state machine (A1) that manages the operation of the electric supercharger system; and a closed-loop controller (I1) consisting of a model-based feedforward function (F1) and a feedback controller (H1) for calculating a desired electric supercharger speed command.

[0104] Feedforward control action of electric mechanical supercharger (n eSC_ff ) is based on a steady-state compressor map provided by the supplier. The compressor map is converted to a corrected mass flow and the expected pressure ratio The desired compressor speed is found using the input from

[0105]

[0106] Mass flow is estimated as the desired cylinder air flow, and the mass flow is then corrected to the reference pressure (P ref ) and reference temperature (T ref ).

[0107]

[0108] The desired boost pressure reference for the electric supercharger is derived from the desired throttle inlet pressure processed by a high pass filter (H1). The frequencies that pass through the high-pass filter are the frequencies to which the turbocharger cannot respond, in other words, the lack of turbocharger capacity. The closed-loop control C1 determines the desired speed command (n eSC C2 is a turbocharger controller for determining the wastegate position (θ wg ). Due to the dynamics between the wastegate and the turbocharger speed, it is usually not necessary to A low pass filter is added for turbocharger control, although one can be added if necessary. Additionally, C2 is designed so that the wastegate saturates during large transients and only adjusts the response when the throttle inlet pressure approaches the desired target. At this point, the control action from C1 is greatly reduced as the high pass filter ensures minimal interaction between the two actuators.

[0109] A proportional feedback controller (H1) is implemented to account for plant model (electromechanical supercharger compressor map) mismatch. Steady-state boost tracking is designed to be delivered by the primary turbocharger. Therefore, there is no integral action in the feedback controller. Since the inner loop electric supercharger speed controller can have different bandwidths for controlling speed in the increasing or decreasing direction, a lead compensator is added to form a closed loop control response.

[0110] The supervisory controller (A1) is used to coordinate the electric supercharger and the electric supercharger bypass valve. The main purpose of the supervisory controller is to determine when to activate and deactivate the electric supercharger and the electric supercharger bypass valve to meet control needs based on system constraints and hardware protection. At a high level, when the activation criteria are met and no system faults are observed, the electric supercharger will be activated and the bypass valve will be closed. Once the deactivation criteria are met or a system fault is observed, the electric supercharger will be deactivated and the bypass valve will be opened.

[0111] The desired boost pressure ratio across the two compressors The measured (eg, achieved) pressure ratio across the turbocharger compressor The pressure ratio across the turbocharger compressor can be controlled by a turbocharger controller C2, which receives as feedback the desired boost pressure ratio across the two compressors and the measured pressure ratio across the turbocharger compressor. The controller C2 then generates a pressure value (θ) for adjusting the degree of opening of the turbocharger wastegate actuator. wg ) signal, which is then sent to turbocharger G2, resulting in a pressure ratio of Thus, the degree of opening of the turbocharger wastegate actuator may be controlled based on the desired boost pressure ratio and the pressure ratio achieved across the turbocharger compressor. For example, as the desired boost pressure ratio increases, the degree of opening of the wastegate actuator may be reduced so as to cause a greater portion of the exhaust gas to flow through the turbocharger turbine instead of through the turbocharger wastegate actuator, thereby increasing the speed of the turbine and, therefore, increasing the pressure ratio across the turbocharger compressor.

[0112] Dynamic distributor D1 uses the pressure ratio across the turbocharger compressor and the total desired boost pressure ratio to calculate the desired pressure ratio for the supercharger compressor For example, using the above function, the desired pressure ratio of the supercharger and the measured pressures P0 and P2 and the desired boost pressure is input into state machine A1, which is a supervisory controller for a discrete event system. State machine A1 determines whether P2 is sufficiently lacking (e.g., greater than a threshold lack) to trigger the start of the electric supercharger. In addition, there are other criteria to ensure that the operation of the electric supercharger does not violate other engine system constraints, for example, due to faults, temperature, power availability, etc. Hysteresis may also be added to the start criteria, such as:

[0113]

[0114] To avoid on / off cycling of the system.

[0115] Once the electric supercharger is triggered, the desired supercharger compressor pressure ratio and the desired mass flow rate are set. is input into the model-based feedforward controller F1. For example, the model-based feedforward controller F1 can look up the corresponding supercharger compressor speed from the compressor map. Then the corresponding supercharger compressor speed n eSC_ff Output to adder element 518.

[0116] The desired supercharger compressor pressure ratio is also compared with the actual supercharger compressor pressure ratio The feedback signal is input into adder element 520 together with the feedback signal, which is subtracted from the desired supercharger compressor pressure ratio as part of the outer loop control C1. The result is input into the error feedback controller to fine-tune the supercharger compressor speed and regulate any inaccuracies in the compressor map. The supercharger compressor speed n generated by the error feedback controller is then eSC_fb The feedback response is input to the adder element 518, which outputs the electric supercharger compressor speed n for a given operating condition. eSCThe electric supercharger compressor speed may be converted into a corresponding electrical signal (eg, duty cycle) that is applied to the electric motor of the electric supercharger G1 to produce a pressure ratio across the supercharger compressor. Therefore, based on and And more specifically, based on and Lack of continuous updates between supercharger compressor speeds.

[0117] Now turn to Figure 6 , which shows an example method 600 for operating a boosted engine system having a turbocharger (e.g., Figure 1 An electric mechanical supercharger (e.g., Figure 1 Here, the turbocharger is configured as a main boosting device, and the supercharger is configured as an auxiliary boosting device.

[0118] At 602, method 200 includes estimating and / or measuring engine operating conditions. For example, the estimated operating conditions may include engine speed, pedal position, operator torque demand, manifold absolute pressure, manifold air flow, manifold air temperature, ambient conditions (such as ambient temperature, barometric pressure and humidity), engine coolant temperature, etc. For example, barometric pressure may be measured by a pressure sensor such as Figure 1 The pressure sensor 58 measures.

[0119] At 604, method 600 includes determining whether boost is requested. In one example, boost may be requested at medium to high engine loads. In another example, boost may be requested in response to an operator pressing an accelerator pedal or an increase in driver torque demand. If boost is not requested, such as when the engine load is low or the driver torque demand is low, method 600 proceeds to 606 and includes operating the engine with natural aspiration (e.g., manifold vacuum). Operating the engine with natural aspiration may include not activating a stepped boost device. For example, an electric motor (e.g., electric motor 108) used to drive an electric mechanical supercharger may not be powered, and a turbocharger wastegate actuator may be commanded to be fully open in order to direct a portion of the exhaust gas to bypass a turbine of the turbocharger (e.g., Figure 1 After 606, method 600 ends.

[0120] If boost is requested at 604, such as in response to a tip-in event, method 600 proceeds to 608 and includes generating a desired pressure ratio (eg, target pressure ratio) command for the turbocharger based on the boost request. The desired pressure ratio for a turbocharger compressor (e.g. Figure 1 The desired outlet pressure of the second compressor 114 (which is also equal to the desired boost pressure (or desired TIP)) is relative to the compressor (eg, Figure 1 For example, P0 may be equal to atmospheric pressure (e.g., as given by Figure 1 of the pressure sensor 58).

[0121] At 610, the method includes decreasing the opening of the turbocharger wastegate based on the total pressure ratio command. For example, as the pressure ratio command increases, the wastegate opening may decrease. In one example, the wastegate is completely closed. By closing the turbocharger wastegate, all of the exhaust gas flow may be directed through the turbocharger turbine, thereby speeding up the rotation of the turbine. Optionally, a compressor recirculation valve (such as Figure 1 The CRV 62 of the turbocharger is closed, so that the pressure loss across the turbocharger compressor is reduced. Thereafter, the compressed air flows to the engine via the turbocharger compressor. At this time, the electric supercharger bypass valve is opened, causing air to flow to the turbocharger compressor while bypassing the supercharger.

[0122] At 612, the method includes calculating a boost pressure deficit at the turbocharger. The boost pressure deficit may be calculated by calculating a boost pressure deficiency. (which is the difference between the desired boost pressure and the measured throttle inlet pressure) and the rate of change of boost pressure deficit For example, as referenced Figure 2 As described, the turbocharger may not achieve the desired boost pressure due to turbo hysteresis. The controller may also determine insufficient air flow at the turbocharger (inlet) corresponding to a lack of boost pressure or use a pressure ratio instead of a delta pressure. In an alternative example, the lack of boost pressure is based on a ratio of the desired boost pressure to the measured throttle inlet pressure instead of a difference. In other words, the lack of boost pressure is based on the desired boost pressure relative to the measured throttle inlet pressure.

[0123] At 614, in response to an indication that there is a lack of boost pressure, the method includes closing the ESBV. By (completely) closing the ESBV, the electric supercharger compressor can be included in the intake air flow path, and the intake air flows to the turbocharger compressor via the electric supercharger. That is, the air flow through the supercharger compressor is increased. In other examples, the ESBV may be closed in response to an amount of boost pressure lack, such as in response to an amount greater than a threshold (such as above which transient boost response is adversely affected). For example, it may be determined whether the absolute amount of boost pressure lack is greater than a threshold, or the rate of change of the boost pressure deficiency is greater than a threshold. Is it greater than a threshold, where the threshold is calibrated as a function of insufficient boost pressure:

[0124]

[0125] Where f2 represents a function. For example, the threshold value may decrease as the boost pressure deficiency increases. The threshold value may define an allowable amount of boost pressure deficiency, above which the peak power and torque performance of the engine may be reduced. Further, a threshold value may be set so that above the threshold value, the amount of additional power and torque provided by operating the electric mechanical supercharger exceeds the amount of electricity consumed by the electric mechanical supercharger. In addition, both the boost pressure deficiency and the rate of change of the boost pressure deficiency may be run through a first-order low-pass filter. By filtering the rate of change of the boost pressure deficiency and / or the boost pressure deficiency, unnecessary starts of the supercharger compressor may be reduced, such as unnecessary starts caused by the driver changing his mind (e.g., applying the accelerator pedal for less than a threshold duration). If the boost pressure deficiency is not greater than the threshold, the ESBV may remain open, the electric mechanical supercharger may remain deactivated, and the compressed air may flow to the engine only via the turbocharger compressor while bypassing the supercharger compressor.

[0126] At 616, in response to the lack of boost pressure, the method includes operating the electric supercharger compressor using electric assist to improve transient boost response. Actuating an electric motor coupled to the supercharger compressor is used to accelerate the supercharger compressor to increase the boost pressure provided to the engine. For example, accelerating the supercharger compressor may include using electric power from a battery (e.g., Figure 1 The power drawn from the system battery 45) is used to rotate the supercharger compressor via the electric motor. Therefore, the supercharger may be able to provide a boost for a limited duration, which is limited by the charge state of the system battery that powers the electric motor. The amount of power (or duty cycle of power) commanded to the electric motor may be based on the pressure ratio allocated to the supercharger, which is a function of the lack. For example, the controller may determine the desired supercharger pressure ratio based on insufficient air flow. The controller may further input the calculated supercharger pressure ratio and MAF into a lookup table to determine the desired supercharger compressor speed. The controller may then input the supercharger compressor speed into an additional lookup table or function to output the motor speed, and the corresponding amount of power (or duty cycle of power) to be provided to the electric motor to produce a target pressure ratio across the supercharger.

[0127] If P1 is greater than P2, the desired supercharger pressure ratio can be clipped To prevent the desired pressure target of the supercharger Overshooting the turbocharger's desired value, which can occur briefly after the throttle is opened. Therefore, the control reference for the supercharger compressor can be described as:

[0128] or

[0129] This is also equal to the turbocharger compressor pressure ratio deficit (or pressure deficit if determined Rather than That is, the supercharger compressor may be controlled based on a turbocharger boost pressure ratio deficiency (or boost pressure deficiency) to provide a desired boost pressure ratio. (or boost pressure ). Thereafter, the compressed air flows to the engine via the turbocharger compressor and the supercharger compressor. In this way, the outlet pressure P2 of the turbocharger compressor includes the pressure generated by both the supercharger compressor and the turbocharger compressor.

[0130] At 618, the method includes determining whether the actual boost pressure achieved at the outlet of the turbocharger is within a threshold of the target boost pressure or TIP. The threshold may be determined as a function of the target TIP or the total commanded pressure ratio, and the threshold may be adjusted to reduce the likelihood of pressure overshoot. For example, at higher pressure ratios, the threshold may be larger.

[0131] If the actual boost pressure is less than the desired TIP by more than a threshold amount, then at 622, the method includes continuing to provide electric assistance via the supercharger while providing steady-state boost pressure via the turbocharger. For example, the controller may maintain or further reduce (if possible) the opening of the wastegate. Additionally, the controller may maintain or further increase (if possible) the motor speed of the electric motor.

[0132] When the actual boost pressure is only a threshold amount below the desired TIP, the controller may apply lead compensation and discontinue electric assistance. Specifically, the motor speed of the electric motor may be reduced to coast the boost pressure to the target TIP with reduced overshoot. Additionally, the controller may transition the motor to a generator mode and operate the generator to apply negative torque on the supercharger compressor, thereby decelerating the supercharger compressor and recovering energy that would otherwise cause a boost pressure overshoot.

[0133] At 624, it can be confirmed that the target boost pressure has been reached. If the target boost pressure has not been reached, then at 626, the method includes further adjusting the wastegate opening and / or the generator speed. For example, the actuator can be adjusted to provide a target speed curve or trajectory to the target boost pressure. Otherwise, if the target boost pressure has been reached, then at 628, the method includes disabling the motor / generator. Among them, the electric motor connected to the supercharger compressor can be disabled by a signal that reduces the motor speed sent from the controller to the electromechanical actuator of the motor. In addition, the ESBV can be actuated open (e.g., fully open) to allow intake air to flow to the engine via the turbocharger compressor while bypassing the supercharger compressor. Thereafter, compressed air can be supplied to the engine only through the turbocharger compressor and not via the supercharger compressor.

[0134] In this way, by instantaneously and dynamically operating the supercharger compressor based on the turbocharger compressor pressure ratio, boost pressure deficiency (e.g., due to a delay in the turbocharger turbine spinning up) is reduced. Further, the amount of time and pumping power of the activated supercharger is minimized, thereby reducing power consumption and improving fuel economy. After 628, the method ends.

[0135] Figure 8 Prophetic example graph 800 depicts dynamic allocation of pressure ratios to provide coordinated turbocharger and electric supercharger control during vehicle operation, such as based on Figure 2 (and Figure 6 ) method and use Figure 5 The accelerator pedal position is shown at curve 802, the actual throttle inlet pressure (TIP) is shown at solid curve 806 relative to the desired TIP at dashed curve 805, and the pressure ratio achieved across the turbocharger compressor is shown at curve 808. With respect to the desired total boost pressure ratio shown in curve 804 The turbine speed of the turbocharger is shown in curve 810, and the pressure ratio achieved across the electric supercharger compressor (ES) is shown in curve 812. The commanded electric supercharger motor speed is shown in curve 816, while curve 817 shows the generator start, the degree of opening of the electric supercharger bypass valve (ESBV) is shown in curve 818, and the degree of opening of the turbocharger wastegate is shown in curve 820. For all of the above, the X-axis represents time, where time increases from left to right along the X-axis. The Y-axis represents the labeled parameter, where the value increases from bottom to top. In this example, the electric supercharger compressor is located upstream of the turbocharger compressor, such as at Figure 1 in the engine system.

[0136] Prior to time t1, the engine is operated without boost (curve 806) due to lower driver demand (curve 802) requiring lower TIP (curve 805). As a result, the actual turbocharger compressor (TC) pressure ratio (curve 808) and the electric supercharger compressor ratio (curve 812) are at baseline amounts (e.g., approximately 1), indicating that since the air is not compressed by either compressor, the pressure upstream of each compressor is equal to the pressure downstream of each compressor. Because the electric supercharger (ES) is not activated, the commanded speed of the electric supercharger compressor remains at zero (curve 816) and the ESBV is fully open (curve 818). As a result, intake air bypasses the electric supercharger compressor instead of being directed to the electric supercharger compressor, as shown in reference Figure 1 Further described, the turbocharger wastegate is fully open (plot 820 ), keeping the turbocharger turbine speed low (plot 810 ) as exhaust gas bypasses the turbine through the open wastegate.

[0137] At time t1, the operator steps on the accelerator pedal, as shown by the increase in accelerator pedal position (curve 802), moving the engine from operation with natural aspiration to operation with boost. The desired amount of boost pressure, as reflected by the rise in the desired TIP (curve 805), is determined based on the amount of torque required by the driver, and the desired total pressure ratio (curve 804) across the boost engine system increases accordingly. The turbocharger is controlled via a command based on the total desired boost pressure ratio. In order to provide the desired total boost ratio in steady state, the turbocharger wastegate is completely closed (curve 820), thereby directing all of the exhaust gas through the turbocharger turbine (rather than through the turbocharger wastegate) in order to speed up the turbine rotation. Therefore, the turbine speed (curve 810) begins to increase. However, due to the slow response time of the turbine speed, the turbocharger cannot achieve the desired total pressure ratio (see the difference between curves 804 and 808) and the desired TIP. The actual turbocharger compressor pressure ratio (plot 808 ) is lower than the desired total boost pressure ratio (plot 804 ) between time t1 and time t2 .

[0138] A pressure ratio deficit at the turbocharger and a corresponding air flow deficit are determined based on the desired total pressure ratio (804) relative to the actual boost pressure ratio (808) at the turbocharger (e.g., based on a difference or based on a ratio as in this example). A pressure ratio corresponding to the air flow deficit is then commanded to the supercharger compressor (curve 812) such that the combination of the pressure ratio across the supercharger compressor (curve 812) and the pressure ratio across the turbocharger compressor (curve 808) together can meet the total desired boost pressure ratio (curve 804). Thus, between t1 and t2, when the turbine speed is low, a larger portion of the total boost pressure ratio is allocated to the supercharger because a smaller portion of the total boost pressure ratio is delivered by the turbocharger.

[0139] In response to the boost pressure deficit being greater than a threshold, the electric supercharger is activated shortly after time t1 to fill the deficit while the turbine spins up. Activating the electric supercharger includes closing the ESBV (curve 818) to direct intake air to the electric supercharger compressor, and powering an electric motor that drives the compressor at a duty cycle that operates the electric motor at a speed (curve 816) based on the boost pressure deficit of the turbocharger compressor. In particular, the speed of the command of the electric motor coupled to the supercharger compressor is selected so that a desired pressure ratio across the supercharger compressor can be provided. As the boost pressure deficit at the turbocharger compressor increases, the desired electric supercharger compressor pressure ratio increases. Between time t1 and time t2, a larger portion of the total boost pressure ratio (curve 806) is provided by the boost pressure generated by the electric supercharger, wherein the electric supercharger pressure ratio increases rapidly (curve 812) as the electric motor is activated. Due to the lower turbocharger turbine speed (plot 810 ), a smaller portion of the total boost pressure ratio is provided by the turbocharger pressure ratio (plot 808 ).

[0140] Between time t1 and time t2, the turbine slowly rotates faster (curve 810). However, the pressure ratio (curve 808) at both ends of the turbocharger compressor continues to lag behind the total achieved boost pressure ratio (curve 806). Between time t2 and time t3, the turbine speed (curve 810) increases faster, wherein the pressure ratio (curve 808) at both ends of the turbocharger compressor increases accordingly and the boost pressure lacks a corresponding decrease. As the pressure ratio (curve 808) at both ends of the turbocharger compressor increases, the pressure ratio at both ends of the supercharger compressor decreases, so that the total boost pressure ratio (curve 806) achieved is equal to the desired boost pressure ratio. Then, once the total boost pressure ratio (curve 806) achieved is close to the desired boost pressure ratio (804), the pressure ratio at both ends of the supercharger compressor gradually decreases (via the regulation of the duty cycle of the electric motor) as the pressure ratio at both ends of the turbocharger compressor increases. Between t2 and t3 , an increased portion of the total boost pressure ratio (plot 806 ) is provided by the boost pressure generated by the turbocharger, while the remainder of the total boost pressure ratio is provided by the boost pressure generated by the electric supercharger.

[0141] At time t3, due to the boost pressure generated by both the turbocharger compressor and the electric supercharger compressor, the actual TIP (curve 806) is within the threshold of the desired TIP (curve 805). To reduce boost pressure overshoot, between t3 and t4, the controller applies lead compensation to close P2 The electric motor speed is reduced before the actual TIP reaches the target TIP. In particular, the electric motor brakes the compressor to reduce the supercharger compressor speed and the ES pressure ratio before the actual TIP reaches the target TIP. The generator command (curve 817) means that the motor is operated in generator mode, which enables energy recovery at the electric motor / generator coupled to the supercharger compressor. The turbocharger wastegate can be activated to open between time t3 and time t4 (curve 820). If this lead compensation is not provided, the TIP will exceed the desired value, resulting in a torque error, and the energy recovery opportunity will be lost.

[0142] At time t4, the turbocharger compressor pressure ratio (curve 808) reaches the desired total pressure ratio (curve 804). Therefore, the desired pressure ratio across the supercharger compressor (curve 812) is reduced to a baseline amount (e.g., approximately 1) and the electric supercharger is deactivated (e.g., no power is supplied to the electric motor driving the supercharger compressor). The ESBV (curve 818) is opened to direct the intake air directly to the turbocharger compressor without directing it to the supercharger compressor, and the commanded electric supercharger speed (curve 816) is reduced to zero. As the supercharger compressor rotates slower, the pressure ratio across the supercharger compressor (curve 812) returns to the baseline. Further, in response to the turbocharger compressor boost pressure ratio (curve 808) reaching the desired boost pressure ratio (curve 804), the degree to which the turbocharger wastegate actuator is opened (curve 820) increases. Thus, turbine speed (plot 810 ) is maintained to provide a desired boost pressure target with feedback regarding the achieved turbocharger compressor boost pressure ratio (plot 808 ).

[0143] At time t5, the accelerator pedal position decreases (curve 802). Therefore, the desired total boost pressure ratio is correspondingly reduced (curve 804). In order to reduce the boost pressure, the turbocharger wastegate actuator (curve 820) is further opened to decelerate the turbocharger turbine (curve 810), and thereby decelerate the turbocharger compressor. Therefore, the pressure ratio achieved across the turbocharger compressor (curve 808) is reduced. Further, because the electric mechanical supercharger is disabled, the turbocharger compressor provides all of the boost pressure.

[0144] At time t6, the accelerator pedal position is further reduced (curve 802), for example, due to a release event. Since boost is no longer requested based on driver demand, the desired total boost pressure ratio (curve 804) is reduced to the baseline. The turbocharger wastegate is fully opened (curve 820) to reduce the boost pressure, thereby further decelerating the turbocharger turbine (curve 810) to the baseline speed. The speed of the turbocharger compressor is correspondingly reduced, thereby reducing the amount of boost pressure generated by the turbocharger compressor. Therefore, the pressure ratio across the turbocharger compressor (curve 808) is reduced to the baseline (e.g., approximately 1). As described above, because the turbocharger compressor provides all of the boost pressure, the total boost pressure ratio (curve 806) is also reduced to the baseline.

[0145] In this way, a turbocharger compressor coupled downstream of a supercharger compressor can be operated via wastegate regulation to provide a total pressure ratio between an inlet of the supercharger compressor and an outlet of the turbocharger compressor based on an operator torque demand, while dynamically adjusting the operation of the supercharger compressor via regulation of an electric motor based on a real-time pressure ratio (or air flow) deficiency at the turbocharger compressor. Here, operating the turbocharger compressor via wastegate regulation can include, as the operator boost demand increases, reducing the opening of the wastegate to spin up the exhaust turbine of the turbocharger and increase the total pressure ratio. In a further example, the real-time pressure (or air flow) deficiency at the turbocharger compressor can be estimated based on an actual pressure ratio across the turbocharger compressor relative to a desired total pressure ratio, and the actual pressure ratio across the turbocharger compressor changes as the exhaust turbine spins up. The engine controller may adjust the operation of the supercharger compressor by increasing the positive motor torque provided from the electric motor to the supercharger compressor to increase the supercharger compressor speed as the air flow deficit increases, while maintaining the actual pressure ratio across the supercharger compressor below a threshold pressure ratio based on the desired total pressure ratio and further based on the actual pressure ratio across the turbocharger compressor. Further, in response to the difference (or ratio) between the actual throttle inlet pressure and the target throttle inlet pressure based on the operator boost demand being above the threshold, the controller may increase the negative motor torque provided from the electric motor to the supercharger compressor to reduce the supercharger compressor speed. In another example, in response to a boost pressure overshoot, the speed of the supercharger compressor may be reduced by providing a negative motor torque from the electric motor while maintaining a reduced opening of the wastegate. In contrast, in response to a boost pressure undershoot, the speed of the supercharger compressor may be increased by providing additional positive motor torque from the electric motor while further reducing the opening of the wastegate. Adjusting operation of the supercharger compressor based on the air flow deficit may include, as examples, adjusting the output of the supercharger compressor independent of a wastegate position and independent of a turbine speed of the turbocharger.

[0146] In this way, while providing boost with the turbocharger of the compound boost system, the electric mechanical supercharger can be started in response to the lack of boost pressure to achieve the desired boost pressure, wherein both the turbocharger and the electric mechanical supercharger are controlled based on the pressure ratio measurement. The technical effect of dynamically adjusting the pressure ratio distribution to the electric mechanical supercharger in real time based on the boost capacity of the turbocharger is that the transient boost response can be improved. In particular, the electric mechanical supercharger can be started only as long as the turbocharger is supported when needed, thereby minimizing the electric assistance drawn from the mechanical supercharger. By saving power usage, fuel economy is improved. By more actively calibrating the pressure ratio commanded to the electric mechanical supercharger and the turbocharger, the boost demand can be more conveniently met. When the boost capacity of the turbocharger is low for the actual boost pressure, the turbo lag can be solved by providing a positive motor torque to the electric mechanical supercharger. When the boost pressure is within the threshold distance of the target pressure, the technical effect of switching to provide a negative motor torque is that the boost pressure can glide to the target pressure without incurring any pressure overshoot. In addition, the energy recovery capability of the electric motor is improved. Overall, the boost pressure can be provided quickly and more efficiently.

[0147] An example method includes: commanding a total pressure ratio of a first compression device of an engine intake device based on an operator torque demand; and adjusting the timing of electric engagement provided to a second compression device of the engine intake device based on an air flow deficit at the first compression device. In the foregoing examples, additionally or optionally, the method further includes adjusting the amount of electric engagement provided to the second compression device of the engine intake device based on the air flow deficit at the first compression device. In any or all of the foregoing examples, additionally or optionally, adjusting the timing and amount of electric engagement to dynamically change the pressure ratio across the second compression device. In any or all of the foregoing examples, additionally or optionally, adjusting includes operating the electric motor in a motor mode to provide a positive motor torque to the second compression device when the air flow deficit at the first compression device is above a threshold, and operating the electric motor in a generator mode to provide a negative motor torque to the second compression device when the air flow deficit at the first compression device is less than a threshold. In any one or all of the foregoing examples, additionally or optionally, providing a positive motor torque to the second compression device includes accelerating the second compression device and increasing the pressure ratio across the second compression device, and wherein providing a negative motor torque to the second compression device includes decelerating the second compression device and reducing the pressure ratio across the second compression device. In any one or all of the foregoing examples, additionally or optionally, the threshold is based on a total pressure ratio commanded to the first compression device, and wherein during electrical engagement, the throttle inlet pressure is below a target boost pressure based on an operator torque demand. In any one or all of the foregoing examples, additionally or optionally, regulating further includes: disabling electrical engagement in response to the throttle inlet pressure being at the target boost pressure. In any one or all of the foregoing examples, additionally or optionally, the first compression device is a turbocharger, the second compression device is an electric mechanical supercharger, and wherein the first compression device is staged downstream of the second compression device in the engine intake. In any one or all of the foregoing examples, additionally or optionally, commanding the total pressure ratio of the first compression device includes adjusting the opening of an exhaust wastegate valve coupled to both ends of an exhaust turbine of the turbocharger. In any or all of the foregoing examples, additionally or optionally, air flow deficiency is estimated in real time based on an actual pressure ratio across the first compression device relative to a commanded total pressure ratio, the actual pressure ratio across the turbocharger compressor changing as the exhaust turbine spins up.

[0148] Another example method includes: regulating operation of a first intake compression device based on a target boost pressure; commanding a positive torque from an electric motor to a second intake compression device when a difference between an outlet pressure of the first compression device and the target boost pressure is above a threshold; and commanding a negative torque from the electric motor to the second intake compression device when the difference is less than a threshold. In the foregoing examples, additionally or optionally, the first intake compression device is a turbocharger having a slower response time than the second intake compressor device, and wherein regulating includes commanding a total pressure ratio of the first intake compression device based on the target boost pressure, and regulating an opening of a wastegate valve coupled across an exhaust turbine of the turbocharger based on the commanded total pressure ratio. In any or all of the foregoing examples, additionally or optionally, when both the positive torque and the negative torque are commanded, the outlet pressure of the first compression device is below the target boost pressure. In any or all of the foregoing examples, additionally or optionally, the method further includes, in response to the outlet pressure of the first compression device being at the target boost pressure, disabling the electric motor. In any or all of the foregoing examples, additionally or optionally, the second compression device is an electric supercharger, and wherein the command includes dynamically varying a pressure ratio across the second compression device via a negative torque or a positive torque while maintaining the pressure ratio across the second compression device less than a desired pressure ratio across the first compression device. In any or all of the foregoing examples, additionally or optionally, commanding a positive torque includes estimating an air flow deficit at the first compression device in real time based on a difference between an outlet pressure of the first compression device and a target boost pressure; and increasing a compressor speed of the second compression device via the positive torque as the estimated air flow deficit increases.

[0149] Another example vehicle system includes: an engine having an intake arrangement; an accelerator pedal for receiving an operator torque demand; a compound boost system including a first supercharger compressor driven by an electric motor receiving power from a battery, and a second turbocharger compressor driven by an exhaust turbine, the second compressor positioned downstream of the first compressor in the engine intake arrangement; a bypass including a bypass valve coupled across the first compressor; a wastegate including a wastegate actuator coupled across the exhaust turbine; and a controller having computer-readable instructions stored on a non-transitory memory for: commanding a total pressure ratio of the second compressor based on the operator torque demand; providing a positive motor torque to increase the pressure ratio of the first compressor when an actual pressure of the second compressor is relatively far from the total pressure ratio; and providing a negative motor torque to reduce the pressure ratio of the first compressor when the actual pressure of the second compressor is relatively close to the total pressure ratio. In the foregoing examples, additionally or optionally, commanding the total pressure ratio includes decreasing an opening of the wastegate actuator to increase an actual pressure ratio across the second compressor as the operator torque demand increases, wherein providing the positive motor torque includes operating the electric motor in a motoring mode based on an air flow shortage for the motor output, the air flow shortage being estimated based on a difference between an actual pressure ratio of the second compressor and the total pressure ratio, and wherein providing the negative torque includes operating the electric motor in a generator mode with a generator output based on the difference. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions for: closing the ESBV while providing the positive motor torque and the negative motor torque. In any or all of the foregoing examples, additionally or optionally, the system further includes: a first pressure sensor, which is connected to the intake device upstream of the first compressor to estimate atmospheric pressure; a second pressure sensor, which is connected to the intake device downstream of the first compressor and upstream of the second compressor to estimate the turbocharger inlet pressure; a third pressure sensor, which is connected to the intake device downstream of the second compressor to estimate the throttle inlet pressure; and wherein the controller includes further instructions for: estimating the total pressure ratio based on the output of the third pressure sensor relative to the output of the first pressure sensor; estimating the actual pressure ratio across the second compressor based on the output of the third pressure sensor relative to the output of the second pressure sensor; and estimating the actual pressure ratio across the first compressor based on the output of the second pressure sensor relative to the output of the first pressure sensor.

[0150] In a further representation, the controller may include further instructions for estimating an actual pressure ratio across the first compressor based on an output of the second pressure sensor relative to an output of the first pressure sensor; estimating an actual pressure ratio across the second compressor based on an output of a third pressure sensor relative to an output of the second pressure sensor; and estimating an overall pressure ratio of the engine intake based on an output of the third pressure sensor relative to an output of the first pressure sensor.

[0151] In another further representation, a method for boosting an engine system includes: directing a total pressure ratio command to a turbocharger; and dynamically adjusting allocation of a portion of the total pressure ratio command to a supercharger based on an air flow deficit at a turbocharger compressor, the air flow deficit being based on turbine speed. In the foregoing examples, additionally or optionally, directing the total pressure ratio command to the turbocharger includes a wastegate adjustment. In any or all of the foregoing examples, additionally or optionally, estimating the air flow deficit relative to the total pressure ratio command based on an actual pressure ratio at the turbocharger, the actual pressure ratio being inferred from turbine speed.

[0152] Note that the example control and estimation procedures included herein can be used with various engine and / or vehicle system configurations. The control methods and procedures disclosed herein can be stored as executable instructions in a non-transitory memory and can be implemented by a control system including a controller in combination with various sensors, actuators, and other engine hardware. The specific procedures described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. In this way, the various actions, operations, and / or functions shown can be performed in the order shown, in parallel, or omitted in some cases. Similarly, the order of processing is not necessary to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown may be repeatedly performed according to the specific strategy used. Further, the described actions, operations, and / or functions can be represented by diagrams to be programmed into the code in the non-transitory memory of a computer-readable storage medium in the engine control system, wherein the described actions are implemented by executing instructions in combination with an electronic controller in a system including various engine hardware components.

[0153] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, because many variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations disclosed herein, and other features, functions, and / or properties.

[0154] The appended claims particularly point out certain combinations and subcombinations believed to be novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include combinations of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presenting new claims in this or a related application. Such claims, whether broader, narrower, equal to, or different in scope from the original claims, are deemed to be included in the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising: operating a first compression device of an engine intake assembly based on an operator torque request; as well as While operating the first compression device: operating the electric motor in a motoring mode to provide positive motor torque to a second compression device of the engine intake when an air flow deficiency at the first compression device is above a threshold; operating the electric motor in a generator mode to provide a negative motor torque to the second compression device when the air flow deficit at the first compression device is less than the threshold; as well as When there is no air flow deficiency at the first compression device, the second compression device is disconnected, bypassed by opening a bypass valve of the second compression device, and compressed air is provided only through the first compression device.

2. The method of claim 1 , wherein providing a positive motor torque to the second compression device comprises accelerating the second compression device and increasing a pressure ratio across the second compression device, and wherein providing a negative motor torque to the second compression device comprises decelerating the second compression device and reducing the pressure ratio across the second compression device.

3. The method of claim 1 , wherein the threshold is based on an overall pressure ratio commanded to the first compression device, and wherein the air flow deficit occurs when a throttle inlet pressure is less than a target boost pressure, wherein the target boost pressure is determined based on the operator torque request.

4. The method of claim 3, wherein the first compression device is a turbocharger, the second compression device is an electric supercharger, and wherein the first compression device is staged downstream of the second compression device in the engine intake. 5 . The method of claim 4 , wherein commanding the overall pressure ratio of the first compression device includes adjusting an opening of an exhaust wastegate valve coupled across an exhaust turbine of the turbocharger.

6. The method of claim 5, wherein the air flow deficit is estimated in real time based on an actual pressure ratio across the first compression device relative to a commanded overall pressure ratio, the actual pressure ratio across the turbocharger changing as the exhaust turbine spins faster.

7. A vehicle system comprising: An engine, the engine having an air intake device; an accelerator pedal for receiving an operator torque request; a compound boost system comprising: a first supercharger compressor driven by an electric motor receiving power from a battery, and a second turbocharger compressor driven by an exhaust turbine, the second turbocharger compressor being positioned downstream of the first supercharger compressor in the engine intake; A bypass, the bypass comprising a bypass valve, the bypass being connected to both ends of the first supercharger compressor; a wastegate, the wastegate including a wastegate actuator, the wastegate coupled to both ends of the exhaust turbine; and a controller having computer readable instructions stored on a non-transitory memory for: commanding an overall pressure ratio of the second turbocharger compressor based on the operator torque demand; adjusting the timing of electrical engagement provided to the first supercharger compressor to provide positive motor torque to increase the pressure ratio of the first supercharger compressor when the actual pressure ratio of the second turbocharger compressor is away from the total pressure ratio; and providing negative motor torque to decrease the pressure ratio of the first supercharger compressor when the actual pressure ratio of the second turbocharger compressor is close to but not equal to the total pressure ratio; and When the actual pressure ratio of the second turbocharger compressor reaches the total pressure ratio, the first supercharger compressor is disabled and the bypass valve is opened to bypass the first supercharger compressor while still providing compressed air via the second turbocharger compressor based on the operator torque demand.

8. The system of claim 7 , wherein commanding the total pressure ratio comprises decreasing an opening of the wastegate actuator to increase the actual pressure ratio across the second turbocharger compressor as the operator torque demand increases, wherein providing the positive motor torque comprises operating the electric motor in a motoring mode with a motor output based on an air flow deficit estimated based on a difference between the actual pressure ratio and the total pressure ratio of the second turbocharger compressor, and wherein providing the negative motor torque comprises operating the electric motor in a generator mode with a generator output based on the difference.

9. The system of claim 8, wherein the controller includes further instructions for: The bypass valve is closed while providing the positive motor torque and the negative motor torque.

10. The system of claim 8, further comprising: a first pressure sensor coupled to the intake device upstream of the first supercharger compressor to estimate barometric pressure; a second pressure sensor coupled to the intake device downstream of the first supercharger compressor and upstream of the second turbocharger compressor for estimating a turbocharger inlet pressure; as well as A third pressure sensor is coupled to the intake device downstream of the second turbocharger compressor for estimating throttle inlet pressure.

11. The system of claim 10, wherein the controller includes further instructions for: estimating the total pressure ratio based on an output of the third pressure sensor relative to the output of the first pressure sensor; estimating the actual pressure ratio across the second turbocharger compressor based on an output of the third pressure sensor relative to the output of the second pressure sensor; and The actual pressure ratio across the first supercharger compressor is estimated based on the output of the second pressure sensor relative to the output of the first pressure sensor.

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