Systems and Methods for Boost Control

Abstract

The present disclosure provides "systems and methods for boost control". Methods and systems are provided for improving surge control in a boosted engine system configured with an electric motor to provide electric boost assist. Surge during accelerator pedal depression and release is addressed by increasing the opening of a compressor recirculation valve and coordinating the recirculation valve opening with adjustments to exhaust wastegate position and power output of the electric motor. The adjustments enable provision of an intake air flow that operates the compressor outside of the surge region while providing a target boost pressure as the driver's torque demand increases or decreases.

Description

Technical Field

[0001] This specification generally relates to methods and systems for coordinated control of an electric assist turbocharger and a continuously variable recirculation valve (CCRV). Background Art

[0002] An engine system can be configured with a supercharging device, such as a turbocharger or a supercharger, to provide boosted charge air and improve peak power output. Using a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, yet with additional fuel economy benefits. However, compressors are prone to surge. For example, when a driver releases the accelerator pedal, the engine intake throttle closes, causing a reduction in forward flow through the compressor, which can lead to compressor surge. Surge can cause noise, vibration, and harshness (NVH) issues, such as undesired noise from the engine intake system.

[0003] By adding electric assist to a turbocharger, the transient response of a boosted engine can be improved. However, this increases the tendency for compressor surge, especially during accelerator pedal maneuvers that require a rapid increase in boost pressure. Conventional methods for controlling surge respond to surge by fully opening a compressor recirculation valve to dump boost pressure from downstream of the compressor to upstream of the compressor, and thus are not suitable for this application.

[0004] Barthelet et al. show an example method for addressing surge in an engine system configured with an electric assist turbocharger in U.S. Patent No. 7,779,634. Therein, in response to an indication of surge, a controller coordinates the operation of a valve in a path that couples an intake passage to an exhaust passage with the operation of an electric assist motor of a boosted engine. This coordinated operation relies on turbocharger speed information to increase the width of the compressor map (i.e., the compressor surge margin) by increasing the air flow from the intake passage to the exhaust passage while controlling the electric motor to maintain or increase compressor rotational speed.

[0005] However, the inventors herein have recognized potential problems with these methods. As an example, introducing fresh air into the exhaust system can cause the exhaust three-way catalyst to be loaded with oxygen, thus unable to properly process the regulated exhaust components, unless additional fuel is injected to burn with the air in the exhaust system. Doing so increases the exhaust system temperature, which must be limited to avoid damaging the turbocharger and the catalyst. The additional fuel also reduces the engine fuel economy. As another example, there may be a situation where there is not a large enough positive pressure difference from the intake end to the exhaust end to generate a large enough flow rate to prevent compressor surge. Depending on the intake and exhaust system design, the pressure difference may be negative under the conditions of interest. In such a case, when the valve is opened, the flow will recycle from the exhaust end to the intake end (i.e., exhaust gas recirculation or EGR). The resulting EGR flow may be beneficial to emissions or fuel economy without reducing the surge margin. As another example, the method relies on the turbocharger speed, but due to cost and / or durability factors, the speed may not be measurable or accurately inferred. SUMMARY OF THE INVENTION

[0006] In one example, some of the above problems can be solved by a method for a supercharged engine, the method comprising: in response to a surge indication after an event of depressing or releasing an accelerator pedal, while maintaining the boost pressure at a certain level based on the torque demand, increasing the surge margin via adjustments to each of the output of an electric motor coupled to a supercharging device and the opening of a continuously variable compressor recirculation valve (CCRV), the adjustments being selected based on the torque demand after the event of depressing or releasing an accelerator pedal. In this way, different airflow adjustments can be provided to address surge in response to an increase in torque demand and surge in response to a decrease in torque demand, thereby improving the performance and responsiveness of the supercharged engine.

[0007] As an example, a supercharged engine can be configured with a turbocharger. In response to an indication of surge, such as surge upon depressing an accelerator pedal, the engine controller can increase the opening of a continuously variable compressor recirculation valve (CCRV) connected across the intake compressor of the turbocharger to increase the surge margin. At the same time, the wastegate opening can be reduced based on the CCRV opening to maintain the boost pressure required by the driver and balance the shaft power. Additionally, the controller can increase the power output of an electric motor coupled to the turbocharger (such as coupled to the shaft of the turbocharger), also referred to herein as electric assist provided by an electric assist motor, to provide the required increase in airflow, thereby increasing the surge margin while also maintaining the required boost pressure and balancing the shaft power.

[0008] Additionally, in the case where the accelerator pedal is released moderately and the driver's torque demand requires the engine to continue operating in a supercharged state, in response to a surge upon releasing the accelerator pedal, the controller can similarly increase the surge margin while maintaining the boost pressure. In the case where releasing the accelerator pedal results in the driver's torque demand being satisfied without using boost pressure, in response to a surge upon releasing the accelerator pedal, the controller can increase the surge margin by the following means: opening a compressor recirculation valve connected across the intake compressor without supplying power to an electric motor coupled to the turbocharger shaft; or extracting power from the electric motor to slow down the turbocharger shaft.

[0009] It should be understood that although the above examples have been described with reference to an engine system in which the supercharging device is a turbocharger, in an alternative example, the supercharging device can be an electromechanical supercharger, and the above adjustments can be performed via an electric motor coupled to the mechanical supercharger compressor.

[0010] In this way, the operation of the compressor recirculation valve can be coordinated with the amount of torque of the electric motor provided to the turbocharger shaft to improve surge control. The technical effect of increasing the CCRV opening while increasing the output of the electric assist motor is that the electric assist motor can be more actively controlled for a faster boost response. This improved boost response may be useful when a surge occurs during an accelerator pedal event when the driver requests an increase in peak torque. Additionally, a robust method for reducing surge while still being able to deliver the desired air flow is provided. By coordinating the operation of both the electric motor and the CCRV in the presence of surge constraints to optimize engine performance, the same motor can be used to improve the surge margin during an accelerator pedal event by increasing torque to the supercharging device (e.g., the turbocharger shaft), and to improve the surge margin during a released accelerator pedal event by subtracting torque from the supercharging device (e.g., the turbocharger shaft). In summary, the performance of the supercharged engine is improved.

[0011] It should be understood that the above Summary of the Invention is provided to introduce a series of concepts in a simplified form, which will be further described in the Detailed Description. The above Summary of the Invention is not intended to define the key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the Detailed Description. Additionally, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 An example embodiment of a supercharged engine system configured with an electric motor for providing electric supercharging assistance is shown.

[0013] Figure 2Depicts an advanced flowchart for solving compressor surge by coordinating the actuation of a compressor recirculation valve with the actuation of an electric assist motor.

[0014] Figure 3 Depicts a predictive example of the coordinated actuation of a continuously variable compressor recirculation valve, the torque of which is delivered by an electric assist motor.

[0015] Figure 4 Shows an example movement of the operating point of a compressor coupled to an electric motor relative to the surge region of the compressor characteristic map.

[0016] Figure 5 Depicts an advanced flowchart of an example method for improving boost pressure control by coordinating the actuation of a compressor recirculation valve with the actuation of an electric assist motor.

[0017] Figure 6 Shows an example boost pressure ratio characteristic map depicting boost pressure control achieved via an electric motor.

[0018] Figure 7 Depicts another predictive example of the coordinated actuation of a continuously variable compressor recirculation valve, the torque of which is delivered by an electric assist motor. Detailed Description

[0019] The following description relates to systems and methods for improving boost pressure control and surge margin in a hybrid vehicle system, the engine of which has a supercharging device configured with electric assist from an electric motor. A non - limiting example of such a system is shown in Figure 1 where an electric turbocharger is provided in a hybrid electric vehicle. The engine controller may be configured to execute control routines, such as the example routine of Figure 2 , to solve surge by coordinating the actuation of a compressor recirculation valve with the adjustment of an exhaust gas valve flap and electric boost assist provided by an electric motor. Predictive examples of coordinating the electric assist motor with CCRV operation in response to surge are shown in Figure 3 . Example movements of the compressor pressure ratio relative to the surge region of the compressor characteristic map in response to CCRV and electric motor actuation are shown in Figure 4 . The engine controller may also be configured to execute control routines, such as the example routine of Figure 5 , to reduce boost pressure overshoot by coordinating the actuation of the CCRV with the adjustment of the torque delivered from the electric assist motor. Predictive examples of coordinating the electric assist motor and CCRV operation to reduce boost pressure overshoot are shown in Figure 7 . Example variations of the compressor pressure ratio in response to CCRV and electric motor actuation during overshoot reduction are shown in Figure 6shown in

[0020] Figure 1 Aspects of an example vehicle system 100 are schematically shown, which vehicle system includes an engine system 101 having an engine 10 coupled in a vehicle 102. In the depicted example, the vehicle 102 is a hybrid electric vehicle having multiple torque sources available for one or more wheels 47. However, in an alternative example, the vehicle system 100 may include a conventional non-hybrid powertrain. In the example shown, the powertrain of the vehicle 102 includes the engine 10 and an electric machine 52. The electric machine 52 may be a motor or a motor / generator. When one or more clutches 53 are engaged, the engine 10 and the electric machine 52 are connected to the wheels 47 via a transmission 48. In the depicted example, a (first) clutch 53 is disposed between the engine 10 and the electric machine 52, and a (second) clutch 53 is disposed between the electric machine 52 and the transmission 48. A controller 12 may send signals to the actuators of each clutch 53 to engage or disengage the clutches, thereby connecting or disconnecting the engine 10 from the electric machine 52 and components connected thereto, and / or connecting or disconnecting the electric machine 52 from the transmission 48 and components connected thereto. For example, when the clutch 53 is engaged, torque from the engine 10 may be transmitted to the wheels 47 via a crankshaft 40, the transmission 48, and a powertrain shaft 84. The transmission 48 may be a gearbox, a planetary gear system, or another type of transmission. The transmission 48 may be a fixed-ratio transmission including multiple gear ratios to allow the engine 10 to rotate at a different speed than the wheels 47. By varying the torque transfer capacity of the first clutch 53 (e.g., clutch slip), the amount of engine torque relayed to the wheels via the powertrain shaft 84 may be adjusted.

[0021] The electric machine 52 may be a hybrid electric vehicle (HEV) motor in a powertrain coupled between the engine and the transmission. In other additional examples, the electric machine 52 may be a crankshaft integrated starter / generator (CISG). The CISG may be coupled to the output shaft of the engine such that during startup of the hybrid vehicle system, the CISG may provide torque to rotate the engine to facilitate starting of the engine. Under some conditions, the CISG may supply torque output to supplement or replace engine torque. Additionally, as described in detail herein, under some conditions, the CISG may supply a negative torque output (i.e., absorb powertrain or engine torque), which negative torque output may be converted into electrical energy, such as for charging the system battery.

[0022] The powertrain can be configured in various ways, including being configured for a parallel, series, or series-parallel hybrid vehicle. In an electric vehicle embodiment, a system electrical energy device such as system battery 45a can be coupled to the powertrain. System battery 45a can be a traction battery, such as a 48V battery, for delivering electrical power to electric motor 52 to provide torque to wheels 47. In some embodiments, electric motor 52 can also operate as a generator to provide electrical power to charging system battery 45a, for example, during a braking operation using regenerative torque. It should be understood that in other embodiments, including non-electric vehicle embodiments, system battery 45a can be a typical starting-lighting-ignition (SLI) battery coupled to alternator 46.

[0023] It should be understood that while system electrical energy storage device 45a is depicted herein as a battery, in other instances, electrical energy storage device 45a can be a capacitor.

[0024] In the depicted embodiment, engine 10 is a supercharged engine configured with a supercharging device (shown herein as turbocharger 15). Turbocharger 15 includes compressor 114 that is mechanically coupled to and driven by turbine 116 via shaft 19, and turbine 116 is driven by the expanding engine exhaust. In one embodiment, the turbocharger can be a twin-scroll device. In another embodiment, the turbocharger can be a variable geometry turbocharger (VGT) where the turbo geometry actively changes in accordance with engine operating conditions. Turbocharger 15 can be further configured as an electric-assisted turbocharger having an electric motor 108 (also referred to herein as an electric assist motor) that is configured to provide electric assistance to the compressor, turbine, or turbocharger shaft. In the depicted example, electric motor 108 is coupled to shaft 19, but in other instances, the electric motor can be selectively coupled to compressor 114 or turbine 116. Electric motor 108 can be powered by an on-vehicle energy storage device such as system battery 45b (as shown, or in an alternative instance, system battery 45a). Electric motor 108 can additionally or alternatively be powered by alternator 46. The amount of power delivered to electric motor 108 can be varied to adjust the duty cycle of the turbocharger. In one instance, the amount of power delivered to electric motor 108 can be increased to increase the speed of compressor 114. As a result of the electric assistance, compressor 114 of turbocharger 15 can rotate quickly, thereby reducing turbo lag.

[0025] It should be understood that although the depicted example shows the turbocharger as a supercharging device and the turbocharger is configured with electric assistance, this is not meant to be limiting. In other alternative examples, the engine can be a compound supercharged engine system that has an electromechanical supercharger (not shown) coupled upstream or downstream of the turbocharger in the engine intake. Here, the mechanical supercharger can be a supercharging device configured to receive electric assistance from the electric motor 108, and the turbocharger 15 can be configured or not configured to receive electric assistance from the electric motor 108. By accelerating the spin of the electromechanical supercharger via the electric motor, a burst of boost pressure can be quickly provided to the engine.

[0026] The electric motor 108 can be configured as a motor - generator. Thus, during conditions where electric assistance is needed to build boost, the electric motor can provide positive torque (also referred to herein as motor torque) to drive the centrifugal compressor of the mechanical supercharger or the turbocharger shaft to improve transient boost pressure delivery. However, the electric motor is also capable of energy recovery by "braking" the motor shaft. Here, negative torque (also referred to herein as regenerative torque) can be applied to the compressor (or shaft or turbine), thereby reducing the compressor speed and simultaneously charging the system battery (such as battery 45b) coupled to the electric motor 108.

[0027] Fresh air is introduced into the engine 10 via the air box 112 along the intake passage 42 and then flows to the compressor 114. Then, the air is compressed at the compressor 114 and introduced into the engine 10. The air compressed by the turbocharger 15 can also be recirculated from downstream of the compressor 114 and downstream of the charge air cooler 18 to the inlet of the compressor 114 through the compressor recirculation passage 60 by adjusting the opening of the continuously variable compressor recirculation valve (CCRV) 62. The CCRV 62 can be a continuously variable valve, and increasing the opening of the CCRV 62 can include actuating (or energizing) a motor or solenoid to open the valve. In an alternative example, the compressor recirculation passage 60 can connect the compressor outlet upstream of the CAC 18 to the inlet of the compressor 114.

[0028] The CCRV 62 can be a continuously variable valve, where the position of the valve is continuously variable from a fully closed position to a fully open position. In some embodiments, the CCRV 62 can be partially open during supercharged engine operation to provide a surge margin. Herein, the partially open position can be the default valve position. Then, in response to an indication of surge, the opening of the CCRV 62 can be increased. For example, the CCRV 62 can be adjusted from the default partially open position towards the fully open position, and the degree of opening is based on an indication of surge (such as compressor pressure ratio, compressor flow rate, differential pressure across the compressor, etc.). In an alternative example, the CCRV 62 can remain closed during boost engine operation (such as peak performance conditions) to shorten the boost response time and increase peak performance.

[0029] The compressor 114 is coupled to the throttle valve 20 via a charge air cooler (CAC) 18 (also referred to herein as an intercooler). Air flows from the compressor 114 through the CAC 18 and the throttle valve 20 to the intake manifold 22. For example, the CAC 18 can be an air-to-air heat exchanger or a water-to-air heat exchanger. A manifold absolute pressure (MAP) sensor 124 can be used to measure the intake manifold pressure (such as the pressure of the air charge within the intake manifold).

[0030] The intake manifold 22 is coupled to a series of combustion chambers 30 via a series of intake valves (not shown). These combustion chambers are further coupled to an exhaust manifold 36 via a series of exhaust valves (not shown). In the depicted embodiment, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold can include multiple exhaust manifold sections. A configuration with multiple exhaust manifold sections can enable the effluents from different combustion chambers to be directed to different locations within the engine system.

[0031] In one embodiment, each of the exhaust valves and intake valves can be electronically actuated or controlled. In another embodiment, each of the exhaust valves and intake valves can be cam actuated or controlled. Whether electronically actuated or cam actuated, the timing of opening and closing of the exhaust valves and intake valves can be adjusted to achieve desired combustion and emission control performance. For example, the cam timing can be adjusted via a variable cam timing system to move the intake cam and exhaust cam to positions that provide optimal volumetric efficiency for a given operating condition.

[0032] The combustion chambers 30 can be supplied with one or more fuels, such as gasoline, alcohol fuel blends, diesel, biodiesel, compressed natural gas, etc. The fuel can be supplied to the combustion chambers 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 of fuel injectors 66 (but Figure 1Only one fuel injector is shown, and each combustion chamber includes a fuel injector coupled thereto). Fuel can be delivered to the fuel injector 66 through a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. Combustion can be initiated in the combustion chamber via spark ignition and / or compression ignition.

[0033] As Figure 1 shown, the exhaust gas from the exhaust manifold 36 is directed to the turbine 116 to drive the turbine. When a reduced turbine torque is desired, a portion of the exhaust gas can alternatively be directed through the wastegate 90, thereby bypassing the turbine. The wastegate actuator 92 (e.g., a wastegate valve) can be actuated to open to release at least some of the exhaust pressure from upstream of the turbine 116 to a location downstream of the turbine 116 via the wastegate 90. By reducing the exhaust pressure upstream of the turbine 116, the turbine speed can be reduced.

[0034] The combined flow from the turbine 116 and the wastegate 90 flows through the emission control device 170. Generally speaking, the emission control device 170 can include one or more exhaust aftertreatment components configured to reduce the amount of one or more substances in the exhaust stream. For example, one exhaust aftertreatment component can be configured to capture NO x from the exhaust stream when the exhaust stream is lean, and reduce the captured NO x when the exhaust stream is rich. In other instances, the exhaust aftertreatment component can be configured to disproportionate NO x or selectively reduce NO x with the aid of a reducing agent. In other additional instances, the emission control device 170 includes a three-way catalyst configured to oxidize residual hydrocarbons and carbon monoxide when reducing NO x in the exhaust stream. Different exhaust aftertreatment catalysts having any such function can be arranged separately or together in a coating or elsewhere in the emission control device 170. In some embodiments, the emission control device 170 can further include a regenerable soot filter configured to capture and oxidize soot particles in the exhaust stream.

[0035] All or part of the treated exhaust gas from the emission control device 170 can be released to the atmosphere via the exhaust pipe 35. However, depending on the operating conditions, some of the exhaust gas can alternatively be diverted to the intake passage 42 via an exhaust gas recirculation (EGR) passage (not shown) including an EGR cooler and an EGR valve. The EGR can be recirculated to the inlet of the compressor 114.

[0036] One or more sensors may be coupled to the inlet of compressor 114. For example, temperature sensor 55 may be coupled to the inlet of compressor 114 to estimate the compressor inlet temperature. As another example, pressure sensor 56 may be coupled to the inlet of compressor 114 to estimate the air pressure entering the compressor. Other additional sensors may include, for example, an air-fuel ratio sensor, a humidity sensor, etc. In other instances, one or more of the compressor inlet conditions (such as humidity, temperature, pressure, etc.) may be inferred based on engine operating conditions. The sensors may estimate the conditions of the intake air received from the intake passage at the compressor inlet, as well as the air charge recirculated through passage 60. One or more sensors may also be coupled to the intake passage 42 upstream of compressor 114 to determine the composition and conditions of the air charge entering the compressor. These sensors may include, for example, pressure sensor 58. In addition, a throttle inlet pressure (TIP) sensor 59 may be coupled downstream of the CAC 18 and upstream of the throttle valve 20 to estimate the boost pressure delivered to the engine.

[0037] During a driver accelerator pedal event, turbo lag may occur when changing from non-boosted engine operation to boosted engine operation (i.e., from non-boosted to boosted accelerator pedal event) in response to an increase in the driver's torque demand. This is because the spin-up of the turbine 116 is delayed due to turbocharger inertia and reliance on exhaust energy to power the turbine. The same may also occur when the engine is operating in boost and the demand for boost instantaneously increases due to an increase in the application of the accelerator pedal by the vehicle driver (i.e., from boost to boost accelerator pedal event). To reduce this turbo lag, during those selected conditions, the turbocharger 15 may be electrically assisted by receiving positive torque from the electric motor 108. Specifically, in response to the accelerator pedal being depressed, the wastegate actuator 92 may close (e.g., fully close) to increase the exhaust flow through the turbine 116. The electric motor may increase the power delivered to the turbocharger shaft until sufficient turbine power is available to rotate the compressor at the speed required to provide the desired boost. When the turbine has sufficient pressure and the flow from the exhaust and the turbocharger can provide the required amount of boost, the electric assist to the turbocharger from the electric motor 108 may be disabled. As referenced Figure 5As described in detail, during accelerator pedal depression, the controller can determine when to disable electric assist to reduce boost overshoot. Additionally, based on the state of charge of the battery connected to the motor, the controller can apply regenerative torque from the motor to reduce boost overshoot. Alternatively, when a supercharger is included in the engine configuration, turbo lag can be reduced by electrically starting the supercharger using positive torque received from the electric motor 108. In particular, an electro-mechanical supercharger compressor that acts faster can be used to improve transient boost response as the turbocharger accelerates.

[0038] During driver release of the accelerator pedal, compressor surge can occur when changing from boosted engine operation to non-boosted engine operation (i.e., a release of the accelerator pedal event from boost to non-boost). This is caused by a reduction in the flow through the compressor 114 when the throttle valve 20 closes during accelerator pedal release. The reduction in forward flow through the compressor can cause surge and degrade the performance of the turbocharger. Additionally, surge can cause noise, vibration, and harshness (NVH) issues, such as undesired noise from the engine intake system. To be able to quickly reduce torque demand in response to accelerator pedal release during the default mode of vehicle operation without causing compressor surge, at least a portion of the air charge compressed by the compressor 114 can be recirculated to the compressor inlet. This allows a large enough flow to continue through the compressor while a reduced flow is delivered to the intake manifold. In particular, the CCRV 62 can be opened to recirculate (cooled) compressed air from the compressor 114 outlet downstream of the CAC 18 to the compressor 114 inlet. In some embodiments, the compressor recirculation system can additionally or alternatively include a recirculation passage for recirculating warm compressed air from the compressor outlet upstream of the CAC 18 to the inlet of the compressor 114. Additionally, the wastegate actuator 92 can be moved to a more open (e.g., fully open) position such that more exhaust flow travels to the exhaust tailpipe while bypassing the turbine, thus accelerating the spin-down of the turbine. As described in reference Figure 2 As described in detail, the controller can coordinate the adjustment of the CCRV position by adjusting the wastegate position to increase the surge margin while also providing the desired boost pressure. For example, the openings of both the CCRV and the wastegate can be increased.

[0039] In addition, during a driver lift-off event, when changing from a supercharged operating condition to a condition of reduced supercharging (i.e., a lift-off event from supercharging to supercharging), compressor surge may occur due to a decrease in the flow rate through the compressor. In cases where supercharging is still required in the new operating condition, the CCRV can be opened by a metered amount to allow a large enough flow rate through the compressor to avoid surge, but not so large as to reduce the supercharging pressure below the required pressure. The compressor can then operate in a state where more turbocharger shaft power is required. Fully closing the wastegate can allow the turbine to provide as much power as possible. If the maximum available turbine power is not sufficient to maintain the compressor operating point, an electric motor can be enabled to provide additional power to the turbocharger shaft. This allows an increase in the surge margin while also allowing the required supercharging pressure to be delivered.

[0040] Compressor surge may also occur during the application of the accelerator pedal because the compressor is operating in the surge region due to a combination of a relatively high pressure ratio and a relatively low flow rate through the compressor. This can occur during rapid transients when the electric motor quickly accelerates the turbocharger. As described in detail with reference to Figure 2 Under such conditions, the controller can coordinate the adjustment of the CCRV position by adjusting the power provided by the electric motor and the wastegate position to increase the surge margin while also providing the desired supercharging pressure. Coordinated control with the CCRV is beneficial for using the motor and wastegate individually because of the variations in the time scales of the three actuators. Specifically, the response of pressure and flow to CCRV adjustment is very fast, while the response resulting from adjusting the motor and wastegate occurs on a slower time scale due to the inertia of the turbocharger. The response to the wastegate may even be slower due to interaction with the exhaust energy.

[0041] The controller 12 can be included in the control system 14. The controller 12 is shown as receiving information from a plurality of sensors 16 (various instances of which are described herein), and sending control signals to a plurality of actuators 81 (various instances of which are described herein). As an example, the sensors 16 can 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, and a TIP sensor 59. Other sensors such as additional pressure sensors, temperature sensors, air-fuel ratio sensors, and component sensors can be coupled to various locations in the vehicle system 100. In addition to or in place of the depicted sensors, the controller can infer or simulate values of pressure, temperature, and / or flow rate based on the operating conditions. The actuators 81 can include, for example, a throttle valve 20, a CCRV 62, an electric motor 108, a wastegate actuator 92, and a fuel injector 66. The controller 12 can receive input data from various sensors, process the input data, and employ various actuators to adjust the engine operation based on the received signals and instructions stored in the controller's memory. The controller can employ these actuators in response to the processed input data based on instructions or code programmed therein corresponding to one or more routines such as the example control routines described herein with respect to Figure 2 the example control routines described. As an example, in response to an indication of surge at the intake compressor when the accelerator pedal is depressed, as inferred from one or more of manifold flow, pedal position, compressor inlet pressure, and boost pressure, the controller can send command signals to the wastegate valve actuator to move the wastegate valve to a more closed position, while sending a command signal to the electric motor to increase the compressor power, and sending a command signal to the CCRV actuator to move the CCRV to a more open position.

[0042] In this way, Figure 1 the components of enable the vehicle system to include: an engine; a turbocharger that includes an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor coupled to the shaft for providing electric assist to the turbocharger; a wastegate that includes a wastegate actuator coupled across the exhaust turbine of the turbocharger; a compressor bypass that includes a continuously variable compressor recirculation valve coupled across the intake compressor of the turbocharger; a pressure sensor coupled to the intake compressor downstream of the compressor for estimating the pressure ratio across the compressor; and a controller for addressing issues associated with torque transients such as surge and boost overshoot.

[0043] For example, the controller can be configured with computer-readable instructions stored on a non-transitory memory to estimate the surge margin of a compressor during a torque transient in response to an input from a pressure sensor; in response to the margin being less than a threshold, increase the opening of a compressor recirculation valve to increase the margin to exceed the threshold; adjust the power output of an electric motor based on the difference between the actual boost pressure when the opening of the compressor recirculation valve increases and the target boost pressure based on the torque transient. For example, when the torque transient includes an accelerator pedal release event from boost to boost, the CCRV opening can be increased by a small amount, and the adjusted power output by the electric motor includes positive motor torque; while when the torque transient includes an accelerator pedal release event from boost to no boost, the opening can be increased by a large amount, and the adjusted power output by the electric motor includes regenerative motor torque. Additionally, when the torque transient includes a slow accelerator pedal press event, the CCRV opening can be increased by a small amount, and the adjusted power output by the electric motor includes a small amount of positive motor torque; while when the torque transient includes a fast accelerator pedal press event, the opening can be increased by a large amount, and the adjusted power output by the electric motor includes a large amount of positive motor torque. The controller can include additional instructions to decrease the opening of an exhaust gas gate actuator when the torque transient includes an accelerator pedal release event or an accelerator pedal press event from boost to boost; and increase the opening of the exhaust gas gate actuator when the torque transient includes an accelerator pedal release event from boost to no boost.

[0044] Additionally, the controller may include instructions for addressing boost overshoot. For example, during a heavy (from boost to boost) accelerator pedal event, the controller may provide positive motor torque from the electric motor for a duration until the actual boost pressure is within a threshold of the desired boost pressure. The controller may then reduce the boost overshoot by a first amount by increasing the opening of the compressor recirculation valve, while further reducing the boost overshoot by a second amount by providing regenerative torque from the electric motor, where the first amount varies relative to the second amount based on each of the following: a predicted amount of boost pressure overshoot after the duration, and the state of charge of the battery. For example, when the state of charge of the battery is above a threshold, the first amount may be adjusted to be higher than the second amount, and when the state of charge of the battery is below the threshold, the second amount may be adjusted to be higher than the first amount. Additionally, the first amount may be further adjusted relative to the second amount based on the surge margin at the accelerator pedal event. The controller may include additional instructions for: predicting the surge margin based on compressor flow using the electric motor that provides regenerative torque, and increasing the first amount as the surge margin decreases. The controller may also include instructions for: maintaining the wastegate valve closed if the actual boost pressure is equal to or below the desired boost pressure after increasing the opening of the CCRV and providing regenerative torque from the electric motor; and increasing the opening of the wastegate valve if the actual boost pressure is above the desired boost pressure after increasing the opening of the CCRV and providing regenerative torque from the electric motor. In this way, during a heavy accelerator pedal event, the wastegate may move to a closed position, the CCRV may move to a slightly open position, and motor torque may be increased to provide positive torque to the turbocharger. When the target boost pressure is reached, the CCRV may quickly open to a greater amount in order to avoid boost pressure overshoot. At the same time, the slower acting turbocharger may be controlled by reducing the electric motor torque to a negative torque point of the turbocharger and by opening the wastegate. When the turbocharger approaches steady state operation under desired operating conditions, the CCRV may be moved to a more closed position.

[0045] Now turning to Figure 2 , method 200 depicts an example routine for controlling a boosted engine having a boosting device configured to provide boosted intake charge. In the depicted method, the boosted engine is a turbocharged engine. The method is capable of addressing compressor surge issues while utilizing coordinated action among a wastegate valve, a compressor recirculation valve, and an electric assist motor. Instructions for performing method 200 and the remainder of the methods included herein may be executed by a controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those referenced above Figure 1The described sensor. According to the method described below, the controller can adjust engine operation by means of an engine actuator of the engine system. It should be understood that although Figure 2 the method is described with reference to a turbocharger, it is not meant to be limited thereto, and in other instances, the method can be applied to an engine having an alternative supercharging device, such as an electromechanical supercharger compressor coupled upstream or downstream of the turbocharger compressor, where the turbocharger itself is or is not enabled with electric assistance.

[0046] At 202, the method includes estimating and / or measuring engine operating conditions. These operating conditions include, for example, the driver's torque demand, engine speed, battery state of charge (SOC), environmental conditions (such as ambient temperature, pressure, and humidity), MAF, MAP, etc.

[0047] At 204, the method includes determining an initial position of each of the following components: an exhaust gas valve flap coupled to an exhaust gas passage of an exhaust gas turbine, and a compressor recirculation valve (such as a continuously variable compressor recirculation valve CCRV) coupled to an intake passage of an intake compressor. In addition, the power to be output by an electric assist motor coupled to a turbocharger (e.g., a turbocharger shaft) can be determined. These determinations can be based on an estimated current operating condition. As an example, as the driver's torque demand increases, the desired boost pressure may increase. Thus, the controller can send a signal to move the exhaust gas valve flap to a more closed position so that a greater portion of the exhaust gas can flow through the turbine, thereby accelerating the turbine spin. In addition, the controller can send a signal to move the CCRV to a more closed position so that the flow recirculation is reduced and the boost pressure is increased. In addition, the exhaust gas valve flap and CCRV adjustments can be coordinated with the electric motor output adjustment to provide the desired boost pressure. Since the electric motor can supply power to the shaft independently of the turbine and the compressor, the coordinated torques from the electric motor and the turbine on the turbocharger shaft can spin the compressor at a speed required to provide the required boost pressure. For example, if the boost pressure required to meet the torque demand is below a threshold, the controller can provide the desired boost pressure only by adjusting the exhaust gas valve flap and CCRV without providing electric assist by an electric motor coupled to the turbocharger shaft. As another example, if the boost pressure required to meet the torque demand is above a threshold, the controller can provide the desired boost pressure by adjusting the exhaust gas valve flap and CCRV while also providing electric assist by an electric motor coupled to the turbocharger shaft. The threshold can be a non-zero positive threshold. Providing electric assist by the electric motor can include the controller sending a control signal (such as a duty cycle signal) to the electric motor to spin the motor at a speed that provides the power corresponding to the requested electric assist to the turbocharger shaft. The controller can refer to a look-up table, an algorithm, or a model that uses the desired boost pressure as an input and provides the corresponding exhaust gas valve flap position, CCRV position, and electric motor power as outputs. Then, the controller can issue command signals to the corresponding actuators based on the determined valve positions and motor power.

[0048] Next, at 206, it can be determined whether there is an accelerator pedal depression event. In one example, if the driver's torque demand increases by an amount greater than a threshold amount, at a rate greater than a threshold rate, and / or in response to depressing the accelerator pedal, an accelerator pedal depression event can be confirmed. If the accelerator pedal depression event is not confirmed, then at 208, it can be determined whether there is an accelerator pedal release event. In one example, if the driver's torque demand decreases by an amount greater than a threshold amount, at a rate greater than a threshold rate, and / or in response to releasing the accelerator pedal, an accelerator pedal release event can be confirmed. In each case, the threshold is a non-zero positive threshold (rate, amount, etc.). If the accelerator pedal release event is confirmed, then at 210, it can be determined whether there is an indication of accelerator pedal release compressor surge. In one example, accelerator pedal release surge may occur due to a sudden decrease in the required air flow through the compressor. As the throttle opening decreases in response to the torque demand at the accelerator pedal release, the air flow through the compressor may decrease. As the air flow through the compressor decreases, the compressor operating point moves closer to the surge limit (i.e., the margin to the surge limit decreases). In one example, an accelerator pedal release surge can be indicated in response to an estimated decrease in air flow, where the estimated decrease in air flow indicates a decrease in the surge limit margin of the compressor. Note that in some cases, the surge may be a soft surge, which manifests as an annoying whooshing noise from the compressor but does not cause a hard surge with violent noise pulses.

[0049] If there is no indication of accelerator pedal release compressor surge, then at 216, the method includes moving the WG and CCRV to their predetermined positions (such as determined at 204), and setting the electric assist motor power to deliver the desired boost pressure. For example, if the desired boost pressure decreases, the CCRV can remain closed if there is a large enough surge margin, and the WG can be moved to a more open position (such as, a fully open position). Additionally, the electric assist motor power can be decreased (e.g., no electric assist power can be provided) or used as a generator to absorb excess torque from the turbocharger shaft (e.g., regenerative torque can be provided).

[0050] If there is an indication of compressor surge upon releasing the accelerator pedal, at 212, the method includes adjusting the motor torque and the CCRV based on the indication of surge. For example, the opening of the CCRV can be increased to provide a large enough surge margin. Since the response to wastegate (WG) changes is later than the onset of surge, the WG can be set at its predetermined position during the adjustment of the motor torque and the CCRV. However, it should be understood that, alternatively, the WG can be set to the fully open position. In one example, as the indication of surge increases (i.e., as the surge margin decreases), the CCRV can move to a more open position. By opening the CCRV, the recirculation flow can increase, resulting in an increase in the forward flow through the compressor. Additionally, opening the CCRV may cause the boost pressure to decrease, thus reducing the pressure ratio across the compressor. Both the increased airflow and the decreased pressure ratio can move the operating point to increase the surge margin. Additionally, the controller can operate the electric motor as a generator to absorb excess torque from the turbocharger shaft. Operating the motor as a generator in this case allows the shaft speed to be reduced more quickly than can be achieved by opening the WG. The WG opening can be adjusted (more open or more closed) to achieve the opening required to achieve the desired boost at the end of releasing the accelerator pedal.

[0051] For example, the controller can first operate the electric motor to absorb excess torque from the turbocharger shaft in order to reduce the boost pressure. At the same time, the controller can increase the opening of the CCRV to adjust the intake airflow and improve the compressor surge margin. Once the compressor reaches the desired operating condition, the motor can be operated in a unidirectional rotation mode, and the CCRV can be closed. In another example, releasing the accelerator pedal can be a change from a boosted state to a less boosted state. The CCRV can be opened to increase the recirculation flow, thus increasing the forward flow through the compressor, to maintain the surge margin. To utilize the additional compressor flow and the reduced exhaust flow to achieve the required boost pressure, the WG can be moved in the closed direction. If the turbocharger shaft power provided by the exhaust turbine is not sufficient to operate the compressor at the desired boost and flow conditions, the electric motor can be operated to add torque to the turbine shaft. In this way, a combination of the CCRV position, the WG position, and the electric motor operating condition can be set to provide the desired boost level and compressor flow rate, so as to operate the engine at the torque required by the driver without compressor surge.

[0052] Return 206. If an accelerator pedal event is confirmed, at 214, it can be determined whether there is an indication of accelerator pedal compressor surge. Note that in some cases, the surge may be a soft surge, which manifests as an annoying whooshing noise from the compressor but does not cause a hard surge with intense noise pulses. In one example, accelerator pedal surge may occur due to an increase in compressor pressure ratio without a sufficient increase in compressor flow rate. This can happen when an electric motor is used to generate a rapid boost transient. For example, in response to an increase in torque demand, the WG can be closed and the electric motor can be operated to increase the torque and speed of the turbocharger shaft. The increase in shaft speed allows the compressor to generate a boost pressure higher than the boost pressure that might occur without using the electric motor. When the engine is still at a relatively low operating speed, this higher boost pressure can reduce the surge margin or cause the compressor to operate in the surge region. In one example, accelerator pedal surge can be indicated in response to an increase in compressor outlet pressure, where the increase in compressor outlet pressure indicates a decrease in the surge limit margin of the compressor.

[0053] If there is no indication of accelerator pedal compressor surge, at 216, the method includes moving the WG to its predetermined position (such as determined at 204). Additionally, as Figure 5 described in detail, the controller can coordinate the adjustment of the CCRV position and the motor torque (positive or negative) of the electric assist motor to deliver the desired boost pressure while reducing boost pressure overshoot. For example, if the desired boost pressure increases, the CCRV can be moved to a partially open position that provides an accelerator pedal surge margin while the positive motor torque provided by the electric assist motor can increase. Then, before the target boost pressure is reached (e.g., when the distance to the desired boost pressure is at a threshold distance), the positive motor torque can be disabled so that the target boost pressure can be reached via the inertia of the motor while increasing the CCRV opening. In addition, based on the ability of the system to accept charge, such as based on the state of charge of the battery connected to the electric assist motor, the controller can apply a negative motor torque or a regenerative torque on the compressor shaft to reduce boost overshoot. For example, when the battery SOC is below the threshold SOC (and thus able to accept charge), the motor can operate as a generator and the CCRV opening can be adjusted based on the motor negative torque to maintain the boost pressure at the target pressure.

[0054] If there is an indication of compressor surge when the accelerator pedal is depressed, at 218, the method includes adjusting the opening of the CCRV based on the indication of surge. For example, as the indication of surge increases, the opening of the CCRV can be increased. In one example, the opening of the CCRV can be increased to increase the air flow rate through the compressor to a threshold air flow rate required to move the compressor outside the surge region of the compressor map. For example, the controller can use the existing pressure ratio and / or surge margin as inputs and can calculate the target air flow rate across the compressor as an output. Then, the controller can further determine the CCRV position corresponding to the target air flow rate and send a control signal to the actuator of the CCRV to move the valve to the determined position (such as by moving the CCRV towards a more open position). By opening the CCRV, the air flow can be recirculated from downstream of the compressor to upstream of the compressor, thereby increasing the forward flow rate through the compressor.

[0055] At 220, the method includes adjusting the opening of the wastegate based on the adjustment of the CCRV in order to maintain boost pressure and balance shaft power. For example, as the opening of the CCRV increases, the opening of the WG can be decreased. By decreasing the opening of the WG, more exhaust can be directed through the turbine, accelerating the turbine spin, thereby increasing compressor torque to meet the required increase in boost pressure at the accelerator pedal depression.

[0056] At 222, it can be determined whether the WG has reached a limit, for example, whether the WG has been fully closed or has been commanded to be fully closed. Once the WG has been commanded to be fully closed, further increasing the boost pressure cannot be provided by adjusting the CCRV and WG individually. If the WG has not been commanded to be fully closed, at 224, the controller can continue to coordinate the adjustment of the WG and CCRV in order to increase the surge margin while maintaining the boost pressure. For example, the controller can continue to increase the opening of the CCRV while decreasing the opening of the WG in order to move the compressor operating point further away from the surge limit while providing the target boost pressure based on the increased torque demand at the accelerator pedal depression.

[0057] If the WG is fully closed or commanded to be fully closed but has not reached that position, at 226, the controller can adjust the electric assist motor power to maintain boost pressure and balance shaft power. For example, the electric assist motor power can be increased by the controller sending a control signal indicating a higher duty cycle to the electric assist motor. The inventors herein have recognized that during an accelerator pedal surge condition, in situations where there may be conflicting requirements, such as the two conflicting requirements of increasing surge margin and increasing torque demand, the combination of turbine power and electric motor power can be coordinated to provide the required air flow to move the compressor further away from the surge limit. In this document, the ability of the electric assist motor to power the turbocharger shaft is independent of the power provided by the turbine to the shaft, and this ability is advantageously used for air flow control during surge. In particular, when the CCRV is opened a metered amount to ensure that the target air flow through the compressor moves away from the surge region of the compressor map, the electric assist motor can be operated to power the turbocharger shaft, causing the compressor to spin at a speed that provides the desired boost level while allowing enough air to flow to address the surge problem. As an example, the controller can estimate the increase in air flow required to increase the compressor surge margin (e.g., based on engine air flow, compressor inlet pressure, boost pressure, etc.). The controller can then increase the opening of the CCRV from the current position based on the difference between the compressor inlet air flow at the current CCRV position and the desired air flow. The controller can then estimate the electric motor torque that needs to be added to the turbine torque to operate the compressor under conditions that will deliver the expected air flow and boost pressure. For example, in response to an increase in engine torque demand, the controller can use a look-up table or an air flow meter to estimate the air flow and determine if that air flow is likely to cause compressor surge. The controller can increase the opening of the CCRV and fully close the WG while increasing the power of the turbo assist motor to operate the compressor to achieve an operating point that provides the required boost and surge margin.

[0058] In one example, the WG can move to the fully open position (or a predetermined position) in response to an indication of an accelerator pedal release surge; and can move to the fully closed position in response to an indication of an accelerator pedal depression surge. In other examples, the opening amounts of the CCRV and the WG can be selected based on engine operating conditions, where the engine operating conditions include engine speed and the scale of accelerator pedal depression or release.

[0059] Thus, the adjustments to the WG, CCRV, and electric assist motor can be coordinated to provide a target air flow that moves the compressor operating point away from the surge region of the compressor map and improves the surge margin. At the same time, the target boost pressure can be provided regardless of whether the surge is caused by an increase or decrease in the required torque.

[0060] In this way, in response to an indication of surge upon depressing the accelerator pedal, the controller can increase the surge margin while maintaining the boost pressure at a certain level based on the driver demand, by adjusting each of the output of the electric motor coupled to the turbocharger shaft and the opening degree of the compressor recirculation valve coupled across the intake compressor. Herein, increasing the margin while maintaining the boost pressure includes increasing the output of the electric motor coupled to the turbocharger shaft while increasing the opening degree of the compressor recirculation valve. In one example, increasing the opening degree of the compressor recirculation valve is to increase the air flow rate through the intake compressor of the turbocharger, and this air flow rate increases as the surge margin decreases. As the difference between the target boost pressure based on the driver demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the output of the electric motor can increase. In one example, increasing the output of the electric motor includes supplying positive motor torque from the electric motor to the turbocharger shaft. Additionally, as the difference between the target boost pressure based on the driver demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the controller can decrease the opening degree of the wastegate valve coupled across the exhaust turbine of the turbocharger. Further, in response to an indication of surge upon releasing the accelerator pedal, the controller can decrease the output of the electric motor while increasing the opening degree of the compressor recirculation valve. As an example, decreasing the output of the electric motor includes supplying negative motor torque or regenerative torque from the electric motor to the turbocharger shaft. As the difference between the target boost pressure based on the driver demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the output of the electric motor can decrease. In some examples, as the difference between the target boost pressure based on the driver demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the controller can also increase the opening degree of the wastegate valve coupled across the exhaust turbine of the turbocharger. In another example, such as an event of releasing the accelerator pedal from boost to boost, as the difference between the target boost pressure based on the driver torque demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the output of the electric motor can increase. Additionally, as the difference between the target boost pressure based on the driver torque demand and the actual boost pressure increases when the opening degree of the compressor recirculation valve increases, the controller can decrease the opening degree of the wastegate valve coupled across the exhaust turbine of the turbocharger. As another example, increasing the opening degree of the wastegate valve in response to an indication of surge upon releasing the accelerator pedal can include fully opening the wastegate valve, and decreasing the opening degree of the wastegate valve in response to an indication of surge upon depressing the accelerator pedal can include fully closing the wastegate valve. In one example, the position of each of the wastegate valve and the compressor recirculation valve can be capable of continuously varying between the fully open position and the fully closed position.

[0061] Now turning to Figure 3, the characteristic line graph 300 depicts an example of coordinated adjustments between the electric assist, CCRV, and WG, which are used to improve the supercharging pressure delivery and the margin of compressor surge. The characteristic line graph 300 depicts the engine torque request at graph line 301, the surge margin achieved as using the strategy depicted at graph line 302, specifically relating to the hard surge region and the soft surge region of the compressor characteristic line graph, and the surge margin without this strategy at graph line 303. The characteristic line graph 300 also depicts the opening of the intake CCRV at graph line 304, the power output of the electric assist motor at graph line 306, the opening of the exhaust wastegate (WG) valve at graph line 308, and the supercharging pressure at graph line 310. All the graph lines are depicted along the x-axis over time.

[0062] Before t1, the engine can operate with a positive supercharging pressure (graph line 310) to a steady torque (graph line 301). At t1, a decelerator pedal event occurs from supercharging to non-supercharging. Without this strategy, the reduction in the flow rate through the compressor will reduce the surge margin to the point where surge will occur (the dashed line of graph line 303). In the depicted strategy, the controller responds by opening the CCRV (graph line 304) by a metered amount to maintain a surge margin (the solid line of graph line 302) that prevents surge from occurring. The wastegate is moved to a more open position to provide the compressor power required at the operating point where there is still supercharging but a smaller supercharging. The electric assist motor is energized to provide additional shaft power to achieve the compressor power required to deliver the required supercharging pressure and flow rate (including the flow rate recirculated through the CCRV). At t2, the wastegate is positioned to deliver supercharging without electric assist, and the supercharging pressure has been reduced to the required level. The electric motor is no longer needed to assist the turbocharger, and its power drops to zero. The engine torque request gradually increases between t2 and t3.

[0063] At t3, a full release of the accelerator pedal occurs (i.e., from a boosted state to an unboosted state), and the torque request is significantly reduced, such as reduced to the idle level 311. Without this strategy, the surge margin would be significantly reduced, and the compressor would operate in the hard surge region. In the depicted strategy, the controller opens the CCRV substantially to avoid hard surge. The opened CCRV rapidly reduces the boost pressure. The wastegate is fully opened to reduce the turbocharger speed and the boost pressure. The electric motor power is reduced to a negative value, causing the motor to act as a generator and absorb energy from the turbocharger shaft, thereby further reducing its speed. The increasing negative value of the power indicates the use of regenerative torque to reduce the turbocharger speed. Specifically, as more regenerative torque is applied, the absolute value of the electric motor torque value, which is negative, becomes larger and larger, and this electric motor torque value moves further away from the zero value. Once the turbocharger speed has been sufficiently reduced at t4, the CCRV closes and the electric motor returns to zero power, thereby prohibiting the application of regenerative torque.

[0064] At t5, a slow press of the accelerator pedal occurs, as indicated by the gradually increasing torque request. With the CCRV remaining closed, the wastegate closes to increase the boost. No electric assist motor is required. At t6, with a rapid increase in the torque request, a rapid press of the accelerator pedal occurs. The electric motor is energized to provide the required boost. The CCRV is opened to provide a large enough airflow to pass through the compressor to avoid the soft surge region. At t7, the engine speed has increased and the airflow consumed by the engine has increased, so the additional flow from the CCRV can be reduced. Also at t7, the turbine power has increased to the point where no electric motor power is needed to provide the required boost.

[0065] Now turning to Figure 4 compressor characteristic map 400, which depicts reducing the pressure ratio across the turbocharger compressor by coordinating the operation of the compressor recirculation valve with the adjustment of the boost assist provided by an electric motor coupled to the turbocharger shaft. Characteristic map 400 shows the compressor pressure ratio (along the y-axis) of the turbocharger compressor at different compressor flow rates (along the x-axis), where the turbocharger compressor has an electric motor coupled to its shaft. Line 402 (solid line) shows the hard surge limit of the turbocharger compressor, while line 404 (dashed line) shows the soft surge limit of the compressor. Solid line 406 (only labeled 1) depicts the constant speed line of the turbocharger compressor. The compressor operating at a flow rate below the hard surge limit 402 results in the turbocharger compressor operating in the hard surge region, while the compressor operating at a flow rate below the soft surge limit 404 and above the hard surge limit 402 results in the turbocharger operating in the soft surge region. The compressor operating in the hard surge region results in poor drivability, objectionable NVH, and potential degradation of engine performance.

[0066] The first decelerator pedal trajectory is depicted at line 408 (narrow dashed line), where no measures are taken to prevent surge in response to decelerating the accelerator pedal. Here, after decelerating the accelerator pedal, the compressor flow first drops into the soft surge region before passing through hard surge. Here, the compressor may spend a significant amount of time in either the hard surge region or the soft surge region, resulting in significant NVH and drivability issues.

[0067] The second decelerator pedal trajectory is depicted at line 410 (medium dashed line), where surge is controlled only by operating a motor that is controlled to the shaft. Here, after decelerating the accelerator pedal, the CCRV remains closed while the motor applies negative or regenerative torque on the shaft, resulting in a reduction in turbine speed. In this example, although hard surge is avoided, the response is not fast enough to avoid soft surge due to the large inertia of the turbocharger and the high state of charge of the battery. Thus, the trajectory deviates from the desired trajectory that is positioned along the soft surge limit. Here, the compressor may spend some time in the soft surge region before the flow increases, resulting in some NVH and drivability issues.

[0068] The third decelerator pedal trajectory is depicted at line 414 (wide dashed line), where surge is controlled by coordinating the opening of the CCRV with the operation of the electric motor. Here, after decelerating the accelerator pedal, the CCRV is opened to a more open position to maintain the trajectory to the right of the soft surge line. The opened CCRV rapidly reduces the boost pressure and increases the compressor forward flow. The electric motor initially operates as a generator to provide negative torque so that energy can be absorbed from the turbocharger shaft and the compressor speed can be rapidly reduced. Once the state of charge of the battery becomes high, regeneration is disabled. The combined action of the CCRV and the motor allows the compressor to operate at the desired pressure ratio while allowing sufficient air flow to avoid soft surge. Thus, the trajectory largely follows the desired trajectory, thereby avoiding NVH and drivability issues.

[0069] Now turning to Figure 5 , an example method 500 is shown that is used to coordinate the operation of the CCRV with the electric assist provided by an electric motor coupled to a turbocharger to reduce boost pressure overshoot. Figure 5 The method of Figure 2 can be included in the

[0070] At 502, as at 202, the method includes estimating and / or measuring engine operating conditions. These operating conditions include, for example, the driver's torque demand, engine speed, battery state of charge (SOC), ambient conditions (such as ambient temperature, pressure, and humidity), MAF, MAP, etc. At 504, as at 204, the method includes determining an initial position of each of the wastegate, CCRV, and the output power of an electric assist motor coupled to the turbocharger. These determinations can be based on the estimated current operating conditions, including the torque demanded by the driver. As an example, as the driver's torque demand increases, the desired boost pressure may increase. Thus, the controller can send a signal to move the wastegate valve (WG) to a more closed position so that a larger portion of the exhaust can flow through the turbine, thus accelerating the turbine spin. In addition to this, the controller can send a signal to move the CCRV to a more closed position, thereby reducing the amount of compressed air allowed to flow back to the compressor inlet. In addition to this, the wastegate and CCRV adjustments can be coordinated with the electric motor output adjustment to provide the desired boost pressure. Since the electric motor can provide power to the shaft independently of the turbine and compressor, the coordinated torque from the electric motor and the turbine on the turbocharger shaft can spin the compressor at the speed required to provide the requested boost pressure. For example, if the boost pressure required to meet the torque demand is below a threshold, the controller can provide the desired boost pressure solely by adjusting the wastegate and CCRV without electric assist from the electric motor coupled to the turbocharger shaft. As another example, if the boost pressure required to meet the torque demand is above a threshold, the controller can provide the desired boost pressure by adjusting the wastegate and CCRV while also providing electric assist from the electric motor coupled to the turbocharger shaft. The threshold can be a non-zero positive threshold. Providing electric assist by the electric motor can include the controller sending a control signal (such as a duty cycle signal) to the electric motor to spin the motor at a speed that provides the electricity corresponding to the requested electric assist to the turbocharger shaft. The controller can refer to a look-up table, algorithm, or model that uses the desired boost pressure as an input and provides the corresponding wastegate valve position, CCRV position, and electric motor power as outputs. The controller can then issue command signals to the corresponding actuators based on the determined valve positions and motor power.

[0071] At 506, the method includes determining whether the actual boost pressure is higher than the desired boost pressure. If the actual boost pressure is higher than the desired value, a boost pressure overshoot condition is confirmed. The desired boost pressure may be based on driver demand, and the actual boost pressure may be inferred or measured via a pressure sensor (such as a throttle inlet pressure (TIP) sensor). In one example, at 506, it may be determined whether boost overshoot has occurred, while in other examples, it may be predicted whether boost pressure overshoot is expected (based on a projection of the current settings). If the actual boost pressure is not higher than the desired value, then at 508, the method includes maintaining the settings of the CCRV, wastegate, and electric assist motor.

[0072] If boost overshoot is confirmed, then at 510, it may be determined whether the battery SOC is higher than a first threshold (threshold 1 or Thr1). Herein, the battery is an energy storage device connected to the electric motor. In an alternative example, the charge acceptance ability of any other energy storage device connected to the electric motor may be determined. The threshold may be a positive non - zero threshold such that when the battery SOC is below the threshold, the battery can accept a large amount of charge. As an example, Thr1 may be calculated as the maximum possible SOC of the current battery condition minus the charge generated by negative motor torque to eliminate the boost differential. If the system can accept charge (e.g., when the battery SOC is less than 30%), then at 512, the method includes applying negative torque or regenerative torque via the electric motor based on the boost pressure differential to reduce the boost overshoot while charging the battery. At the same time, the positions of the wastegate and CCRV may be maintained. For example, both the wastegate and CCRV may be maintained closed or nearly closed such that the turbocharger compressor can continue to provide the boost demand while the electric motor absorbs the excess boost. In another example, if the negative torque provided via the electric motor is at its limit (such as when the battery cannot accept any additional charge) and there is still some boost overshoot, the CCRV may be opened a certain amount based on the remaining overshoot while maintaining the wastegate closed to continue providing a large enough boost pressure.

[0073] If the battery SOC is higher than a first threshold, it can be determined whether the battery SOC is also higher than a second threshold (threshold 2 or Thr2), higher than the first threshold at 514. As an example, Thr2 can be 80% SOC. When the battery SOC is higher than Thr2, the battery cannot accept charging. When the battery SOC is lower than Thr2, the battery can accept some charge, but this charge is less than the amount of charge that can be accepted at 512. As an alternative, at 514, it can be determined whether the battery can accept any charge. If the system can accept any charge (e.g., when the battery SOC is less than 80%), then at 518, the method includes applying negative torque or regenerative torque via an electric motor based on the SOC margin to reduce boost and charge the battery. That is, the regenerative torque output by the motor can be limited based on the limited charge acceptance potential of the battery (at higher SOCs), and the battery can be charged accordingly. Then the boost pressure difference can be resolved by opening the CCRV. Specifically, the remaining boost overshoot after operating the electric motor with regenerative torque is resolved by increasing the opening of the CCRV according to the remaining overshoot. At the same time, the wastegate remains closed to allow the boost engine performance to remain elevated.

[0074] Returning to 514, if the battery SOC is higher than Thr2 and thus cannot accept charge, then in view of the limited charging potential of the battery, at 516, the boost pressure overshoot is resolved according to the boost overshoot by opening the CCRV.

[0075] In this way, taking into account the charge acceptance potential of the system battery, the regenerative torque output by the electric assist motor can be coordinated with the opening of the CCRV to reduce the boost pressure overshoot without degrading the boost engine performance.

[0076] Reference Figure 6 Characteristic line graph 600 shows an example of reducing the boost pressure overshoot by coordinating the CCRV with the electric motor torque. Characteristic line graph 600 depicts the boost pressure along the y-axis and time along the x-axis. The actual boost pressure response achieved via the strategy discussed above is shown at plot line 602. The boost pressure response without the current strategy is shown at plot line 604. The detuned boost pressure response is shown at plot line 606.

[0077] Before t1, due to an increase in torque demand, the engine operates in a supercharged state. Specifically, the engine operates with electric supercharger assistance (including positive motor torque from an electric motor coupled to the compressor) to raise the boost pressure to a desired level. At t1, once the actual boost pressure is at or within a threshold of the desired boost level, the electric motor is disabled. If the boost pressure is actively controlled via the electric assist motor and a closed wastegate to achieve fast response, the actual boost pressure may exceed the desired pressure after the motor is disabled due to the inertia of the turbocharger, as shown at trace 604. On the other hand, if the response of the electric motor is detuned to reduce boost pressure overshoot, the actual boost pressure can reach the desired level slowly, as shown at trace 606, and the boost performance improves slowly, which may make the engine appear sluggish.

[0078] In the depicted strategy, instead of turning off the motor at t1, the operation of the CCRV and the motor is coordinated to reduce boost pressure overshoot while providing an actual boost profile 602 that matches the desired boost profile. Specifically, between t1 and t2, if the state of charge of the battery is below a threshold, the CCRV can remain closed to allow improvement in boost response while negative torque is applied from the electric motor due to overboost. Then at t2, once the boost overshoot is resolved, the motor can be disabled. Alternatively, if the state of charge of the battery is above the threshold, the motor can remain off and the CCRV can be opened between t1 and t2 in response to overboost.

[0079] Now turning to Figure 7 , characteristic plot 700 depicts an example of coordinated adjustments between the electric assist provided by the electric motor, the CCRV, and the WG to improve boost pressure delivery and the margin against compressor surge. Characteristic plot 700 depicts the engine torque request at trace 701, the surge margin achieved using the strategy depicted at trace 702, specifically relating to the hard surge region and the soft surge region of the compressor characteristic plot, and the surge margin without the strategy at trace 703. Characteristic plot 700 also depicts the opening of the intake CCRV at trace 704, the power output of the electric assist motor at trace 706, the opening of the exhaust wastegate (WG) valve at trace 708, the boost pressure at trace 710, and the state of charge (SOC) of the battery coupled to the electric assist motor at trace 712. All traces are depicted along the x-axis over time.

[0080] Before t1, the engine can operate with a low amount of positive boost pressure (line 710) at a steady low level of torque (line 701). At t1, an accelerator pedal event from boost to boost occurs. The WG is reduced (line 708) to accelerate the turbocharger and increase the boost pressure output. As the turbine and compressor of the turbocharger accelerate, electric assist from the electric motor is provided in the form of positive motor torque to meet the instantaneous increase in boost demand (line 706). In particular, the motor operates for a duration from t1 to t2, and then, once the boost pressure is within the threshold of the desired boost pressure, the motor can be deactivated and no longer provide electric assist.

[0081] However, due to the inertia of the turbocharger, there is a possibility of boost overshoot even after the motor is turned off (dashed line 711). In addition, a boost pressure greater than desired can cause accelerator pedal surging (line 703). To address the issues of boost overshoot and surging, coordinated adjustments are made between the CCRV and the electric assist. These adjustments are based on the ability of the electric motor to accept charge as inferred from the SOC of the battery. At t2, since the battery has a low SOC (line 712) and thus a high charge acceptance capacity, a large portion of the boost overshoot is addressed by providing negative regenerative torque from the motor to the turbocharger shaft. As shown, the amount of regenerative torque provided increases, resulting in an increasing absolute value of the negative torque and moving further away from the zero torque level in the negative direction. At the same time, a smaller portion of the boost overshoot is addressed by increasing the opening of the CCRV. While the negative torque from the motor addresses the boost overshoot, the opening of the CCRV is slightly opened to increase the compressor surge margin when operating with negative torque. By only slightly increasing the opening of the CCRV and maintaining the WG in a more closed state, the boost pressure can be maintained at a high enough level to meet the torque demand.

[0082] At t3, a decelerator pedal event from boost to boost occurs. Without coordinated adjustment, a reduction in the flow rate through the compressor would reduce the surge margin to a point where surging would occur (dashed line in line 703). In the depicted strategy, the controller responds by opening the CCRV a measured amount to maintain a surge margin that prevents surging. The wastegate is moved to a more open position to provide the compressor power required at the still-boosted operating point. The electric assist motor is energized to provide additional shaft power to achieve the compressor power required to deliver the desired boost pressure and flow rate (including the flow rate recirculated through the CCRV). At t4, the boost pressure has been reduced to the desired level. Since the surge margin is sufficient and there is no recirculated airflow, the CCRV closes. The electric motor is no longer needed to assist the turbocharger, and its power drops to zero.

[0083] Between t4 and t5, the torque level is stable. The wastegate and CCRV openings are maintained. The motor remains disabled. At t5, another accelerator pedal event from boost to boost occurs. The opening of the WG is decreased to accelerate the turbocharger and the boost pressure output is increased. As the turbine and compressor of the turbocharger accelerate, electric assist from the electric motor is provided in the form of positive motor torque to meet the instantaneous increase in boost demand (graph line 706). In particular, the motor operates for the duration from t5 to t6 and then, once the boost pressure is within the threshold of the desired boost pressure, the motor can be deactivated and no longer provide electric assist. During the accelerator pedal press, the CCRV is opened to prevent soft surge of the compressor.

[0084] However, due to the inertia of the turbocharger, there is a possibility of boost overshoot even after the motor is turned off. To address the issues of boost overshoot and surge, coordinated adjustments are made between the CCRV and the electric assist. These adjustments are based on the ability of the electric motor to accept charge as inferred from the SOC of the battery. At t6, since the battery has a high SOC and thus a low charge acceptance capacity, a larger portion of the boost overshoot is addressed by opening the CCRV while the remaining smaller portion of the boost overshoot is addressed using the regenerative torque provided by the motor to the turbocharger shaft. At the same time, the smaller portion of the boost overshoot is addressed by increasing the opening of the CCRV. In particular, the regenerative torque from the motor is adjusted based on the limited ability of the battery to accept charge and the CCRV opening is increased by a large amount to address the remaining portion of the boost overshoot and improve the surge margin of the compressor. By increasing the opening of the CCRV by a large amount when the battery SOC is high and maintaining the WG closed, the boost pressure can be maintained at a high enough level to meet the torque demand while addressing the boost overshoot.

[0085] At t7, there is a decelerator pedal event from boost to non-boost. The controller responds by opening the CCRV and the wastegate while the motor remains disabled.

[0086] It should be understood that although the above routines have been discussed with reference to an electric turbocharged engine system, in other instances, the engine may be a multi-stage supercharged engine system having an electric supercharger compressor serially coupled (either upstream or downstream) with a turbocharger compressor. Wherein, opening the CCRV in a metered amount can increase the airflow to the multi-stage compressor. If no additional turbine power is available at the turbocharger, the turbocharger will tend to use the increased air flow to reduce the pressure ratio. In such a case, additional power can be provided to the electric compressor to increase the pressure ratio so as to generate the same total pressure at the intake manifold. Since the turbocharger of the multi-stage supercharged engine system tends to experience higher airflows and lower pressure ratios, surging is less likely to occur.

[0087] In this manner, a coordinated operation of the compressor recirculation valve, the wastegate valve, and the motor torque from the electric assist motor can be used to provide the desired airflow to improve the surge margin during torque transients (including during accelerator pedal depression and accelerator pedal release). The technical effect of increasing the CCRV opening while increasing the output of the electric assist motor is that the CCRV can be opened to a greater extent to quickly relieve surging without causing a sluggish engine response when surging occurs during peak power demand. Additionally, the CCRV allows surging to be relieved by keeping the wastegate more closed and / or closed for a longer duration. By enabling the delivery of the desired airflow through coordinated adjustment of the CCRV, the electric assist motor, and the WG, surging can be relieved more quickly, thereby reducing surge-related NVH issues. In summary, the boost engine response and the ability to mitigate surging are improved. In addition to this, the coordinated operation of the compressor recirculation valve and the electric assist motor enables better resolution of boost overshoot during accelerator pedal depression. By adjusting the proportion of overboost resolved via the CCRV opening relative to the overboost resolved using negative torque from the motor based on the state of charge (SOC) of the battery, boost overshoot can be resolved more effectively while also managing the battery SOC.

[0088] In one example, a method includes: in response to a surge indication after an accelerator pedal press or release event, while maintaining the boost pressure at a certain level based on the torque demand, increasing the surge margin by adjusting each of the output of an electric motor coupled to a boosting device and the opening of a continuously variable compressor recycle valve (CCRV), where these adjustments are selected based on the torque demand after the accelerator pedal press or release event. In the foregoing example, in addition or alternatively, when the torque demand after the accelerator pedal press or release is higher than a threshold demand, these adjustments include increasing the positive torque of the electric motor output while increasing the CCRV opening, and when the torque demand after the accelerator pedal press or release is lower than the threshold demand, these adjustments include increasing the regenerative torque of the electric motor output while increasing the CCRV opening. In any or all of the foregoing examples, in addition or alternatively, when the torque demand is higher than the threshold demand, the engine operates with boost; and when the torque demand is lower than the threshold demand, the engine operates with natural aspiration. In any or all of the foregoing examples, in addition or alternatively, the adjustment of each of the electric motor output and the CCRV is further based on the state of charge of a battery coupled to the electric motor. In any or all of the foregoing examples, in addition or alternatively, when the torque demand after the accelerator pedal press or release is lower than the threshold demand, the regenerative torque of the electric motor output increases by a greater amount as the state of charge of the battery decreases, and wherein the increase in the CCRV opening is adjusted based on the increase in the regenerative torque of the electric motor output. In any or all of the foregoing examples, in addition or alternatively, when the torque demand after the accelerator pedal press or release is higher than the threshold demand, the opening of the CCRV is based on the surge margin, and the positive torque of the electric motor output is based on a target boost pressure, which is based on the torque demand relative to the actual boost pressure and the adjusted CCRV opening, and wherein when the torque demand after the accelerator pedal press or release is lower than the threshold demand, the opening of the CCRV is based on the surge margin, and the regenerative torque of the electric motor output is based on a target boost pressure, which is based on the torque demand relative to the actual boost pressure and the adjusted CCRV opening. In any or all of the foregoing examples, in addition or alternatively, the opening of the CCRV increases as the surge margin decreases, wherein the positive torque of the electric motor output increases as the target boost pressure based on the torque demand exceeds the actual boost pressure with the adjusted opening of the CCRV, and wherein the regenerative torque of the electric motor output increases as the actual boost pressure exceeds the target boost pressure based on the torque demand with the adjusted opening of the CCRV.In any or all of the foregoing instances, in addition to or alternatively, the supercharging device includes one of an electromechanical supercharger and a turbocharger, wherein when the supercharging device is a turbocharger, an electric motor is coupled to one of the shaft, an intake compressor, and an exhaust turbine of the turbocharger, wherein the opening of the compressor recirculation valve is increased to increase the air flow through the intake compressor of the turbocharger, and the method further includes adjusting the position of the wastegate valve coupled to the exhaust turbine based on the torque demand after an accelerator pedal depression or release event. In any or all of the foregoing instances, in addition to or alternatively, when the torque demand after an accelerator pedal depression or release is higher than a threshold demand, the wastegate valve is closed, and wherein when the torque demand after an accelerator pedal depression or release is lower than the threshold demand, the wastegate valve is opened.

[0089] Another example method includes: in response to a first release of the accelerator pedal to boosted engine operation, while increasing the power output of an electric motor coupled to an intake compressor of a turbocharger, opening a continuously variable compressor recirculation valve (CCRV) by a first amount; and in response to a second release of the accelerator pedal to unboosted engine operation, while decreasing the power output of the electric motor, opening the CCRV by a second amount that is greater than the first amount. In the foregoing example, in addition or alternatively, increasing the power output of the electric motor includes providing positive motor torque from the electric motor to the compressor, and wherein decreasing the power output of the electric motor includes providing regenerative motor torque from the electric motor to the compressor. In any or all of the foregoing examples, in addition or alternatively, during the first release of the accelerator pedal, the first opening amount of the CCRV is based on the surge margin of the compressor, and wherein the positive motor torque is based on the torque demand after the first release of the accelerator pedal, and wherein during the second release of the accelerator pedal, the second opening amount of the CCRV is based on the surge margin of the compressor, and wherein the regenerative motor torque is based on the torque demand after the second release of the accelerator pedal. In any or all of the foregoing examples, in addition or alternatively, during the first release of the accelerator pedal, the first amount increases as the surge margin decreases, and the positive motor torque increases as the target boost pressure based on the torque demand after the first release of the accelerator pedal exceeds the actual boost pressure when the CCRV opening is the first amount; and wherein during the second release of the accelerator pedal, the second amount increases as the surge margin decreases, and the regenerative motor torque increases as the target boost pressure based on the torque demand after the second release of the accelerator pedal drops below the actual boost pressure when the opening is the second amount. In any or all of the foregoing examples, in addition or alternatively, the method further includes, during the first release of the accelerator pedal, decreasing the opening of an exhaust gas wastegate of an exhaust turbine coupled to the turbocharger, the opening further decreasing as the target boost pressure exceeds the actual boost pressure when the CCRV opening is the first amount, and wherein during the second release of the accelerator pedal, increasing the opening of the exhaust gas wastegate, the opening further increasing as the target boost pressure drops below the actual boost pressure when the CCRV opening is the second amount. In any or all of the foregoing examples, in addition or alternatively, the method further includes closing the CCRV and disabling the electric motor when the actual boost pressure reaches the target boost pressure after each of the first release of the accelerator pedal and the second release of the accelerator pedal. In any or all of the foregoing examples, in addition or alternatively, the method further includes: in response to a faster depression of the accelerator pedal than a threshold to boosted engine operation, opening the CCRV while increasing the power output of the electric motor, the opening of the CCRV being based on the surge margin, and increasing the power.

[0090] Another example vehicle system includes: an engine; a turbocharger including an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor coupled to the shaft for providing electric assist to the turbocharger; a wastegate including a wastegate actuator coupled across the exhaust turbine of the turbocharger; a compressor bypass including a continuously variable compressor recirculation valve (CCRV) coupled across the intake compressor of the turbocharger; a pressure sensor coupled to the intake system downstream of the compressor for estimating the pressure ratio across the compressor; and a controller having computer-readable instructions stored on a non-transitory memory for: estimating a surge margin of the compressor during a torque transient in response to an input from the pressure sensor; increasing the opening of the CCRV to increase the margin above a threshold in response to the margin being less than the threshold; and adjusting the power output of the electric motor based on a difference between an actual boost pressure at the increased CCRV opening and a target boost pressure based on the torque transient. In the foregoing example, in addition or alternatively, when the torque transient includes a throttle pedal release event from boost to boost, the CCRV opening is increased by a smaller amount, and the adjusted power output by the electric motor includes positive motor torque, wherein when the torque transient includes a throttle pedal release event from boost to no boost, the CCRV opening is increased by a larger amount, and the adjusted power output by the electric motor includes regenerative motor torque. In any or all of the foregoing examples, in addition or alternatively, when the torque transient includes a slow throttle pedal depression event, the CCRV opening is increased by a smaller amount, and the adjusted power output by the electric motor includes a smaller amount of positive motor torque, and wherein when the torque transient includes a fast throttle pedal depression event, the CCRV opening is increased by a larger amount, and the adjusted power output by the electric motor includes a larger amount of positive motor torque. In any or all of the foregoing examples, in addition or alternatively, the controller includes additional instructions for: decreasing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event or a throttle pedal depression event from boost to boost; and increasing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event from boost to no boost.

[0091] Another example method includes: in response to a predicted boost overshoot, adjusting each of a regenerative torque output by an electric motor coupled to a boosting device and an opening degree of a continuously variable compressor recirculation valve (CCRV), the adjustment being based on a state of charge (SOC) of a battery coupled to the electric motor. In the foregoing example, in addition or alternatively, the method further includes predicting a boost overshoot after an increase in torque demand, wherein a positive torque is output by the electric motor. In any or all of the foregoing examples, in addition or alternatively, the adjustment includes increasing the regenerative torque output by the electric motor as the state of charge of the battery decreases at the predicted boost overshoot, and increasing the opening degree of the CCRV as the regenerative torque output by the electric motor decreases. In any or all of the foregoing examples, in addition or alternatively, the adjustment includes: when the state of charge of the battery is low, increasing the regenerative torque output by the electric motor according to a boost pressure difference of the predicted boost overshoot, and increasing the opening degree of the CCRV as a surge margin of a compressor operating with a regenerative torque output applied via the electric motor decreases; and when the state of charge of the battery is high, increasing the opening degree of the CCRV as the boost pressure difference of the predicted boost overshoot increases, and increasing the regenerative torque output by the electric motor as the surge margin of a compressor operating with an increased CCRV opening degree decreases. In any or all of the foregoing examples, in addition or alternatively, the boost pressure difference of the predicted boost overshoot includes a difference between a target boost pressure based on torque demand and an actual boost pressure, and a rising rate of the difference. In any or all of the foregoing examples, in addition or alternatively, the adjustment includes: when the SOC is below a first threshold, increasing the regenerative torque output by the electric motor while opening the CCRV by a first amount; when the SOC is higher than the first threshold but lower than a second threshold, increasing the regenerative torque output by the electric motor by a second amount smaller than the first amount while opening the CCRV by a second amount greater than the first amount; and when the SOC is higher than each of the first threshold and the second threshold, disabling the electric motor while opening the CCRV by a third amount greater than the second amount, wherein the second threshold is higher than the first threshold. In any or all of the foregoing examples, in addition or alternatively, the boosting device includes one of an electric supercharger and a turbocharger, wherein when the boosting device is a turbocharger, the electric motor is coupled to one of a shaft of the turbocharger, an intake compressor, and an exhaust turbine, and the method further includes: maintaining a wastegate valve coupled across the exhaust turbine closed during the adjustment. In any or all of the foregoing examples, in addition or alternatively, adjusting the opening degree of the CCRV includes adjusting the opening degree from an initial position based on an increase in torque demand. In any or all of the foregoing examples, in addition or alternatively, the boosting device is a turbocharger, wherein an intake compressor of the turbocharger is coupled to the exhaust turbine, and the method further includes: maintaining a wastegate valve coupled across the exhaust turbine at a certain position based on an increase in torque demand during the adjustment.

[0092] Another example method for a supercharged engine includes: in response to a first supercharging overshoot condition, increasing the opening degree of a continuously variable compressor recirculation valve (CCRV) while increasing the regenerative torque output by an electric motor of an intake compressor coupled to a supercharging device; in response to a second supercharging overshoot condition, maintaining the opening degree of the CCRV while increasing the regenerative torque output by the electric motor. In the foregoing example, in addition or alternatively, during each of the first supercharging overshoot condition and the second supercharging overshoot condition, a margin above a compressor threshold is maintained from a surge limit. In any or all of the foregoing examples, in addition or alternatively, during the first condition, the state of charge of a battery coupled to the electric motor is relatively high; during the second condition, the state of charge of the battery is relatively low. In any or all of the foregoing examples, in addition or alternatively, during the first condition, increasing the regenerative torque output by the electric motor is based on the difference between the state of charge of the battery and a threshold state of charge, the regenerative torque further increases as the difference increases, and wherein increasing the opening degree of the CCRV is based on the amount of supercharging overshoot remaining after operating with the increased regenerative torque, and the opening degree of the CCRV further increases as the amount of supercharging overshoot increases. In any or all of the foregoing examples, in addition or alternatively, the method further includes, during a third condition, with the state of charge of the battery being higher than the state of charge during each of the first condition and the second condition, maintaining the electric motor disabled while increasing the opening degree of the CCRV based on the amount of supercharging overshoot. In any or all of the foregoing examples, in addition or alternatively, the supercharging device is a turbocharger, the turbocharger includes a compressor coupled to an exhaust turbine, and the method further includes maintaining a wastegate valve coupled across the exhaust turbine of the turbocharger closed during each of the first condition, the second condition, and the third condition.

[0093] Another example vehicle system includes: an engine; a turbocharger that includes an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor coupled to the shaft for providing an electric assist to the turbocharger, the electric motor being driven by a battery; a wastegate that includes a wastegate actuator coupled across the exhaust turbine of the turbocharger; a compressor bypass that includes a continuously variable compressor recirculation valve (CCRV) coupled across the intake compressor of the turbocharger; and a controller having computer-readable instructions stored on a non-transitory memory, the instructions for: in response to an accelerator pedal event from boost to boost, providing positive motor torque by the electric motor for a duration until the actual boost pressure is within a threshold of the desired boost pressure; then, reducing boost overshoot by a first amount by increasing the opening of the compressor recirculation valve, while further reducing boost overshoot by a second amount by providing negative torque by the electric motor, the first amount varying relative to the second amount based on each of a predicted amount of boost pressure overshoot and a state of charge of the battery after the duration. In any or all of the foregoing examples, additionally or alternatively, when the state of charge of the battery is above a threshold, the first amount is higher than the second amount, and when the state of charge of the battery is below the threshold, the second amount is higher than the first amount. In any or all of the foregoing examples, additionally or alternatively, the first amount is further adjusted relative to the second amount based on a surge margin at the accelerator pedal event. In any or all of the foregoing examples, additionally or alternatively, the further adjustment includes using the electric motor that provides negative torque, predicting a surge margin based on compressor flow, and increasing the first amount as the surge margin increases. In any or all of the foregoing examples, additionally or alternatively, the controller includes additional instructions for: maintaining the wastegate valve closed if, after increasing the opening of the CCRV and providing negative torque by the electric motor, the actual boost pressure is equal to or lower than the desired boost pressure; and increasing the opening of the wastegate valve if, after increasing the opening of the CCRV and providing negative torque by the electric motor, the actual boost pressure is higher than the desired boost pressure.

[0094] In an additional representation, the engine is configured in a hybrid electric vehicle system. In yet another additional representation, the engine is configured in a vehicle that can be autonomously driven.

[0095] Note that the example control routines and estimation routines included herein can be used with a variety of engine configurations and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. processing strategies. Accordingly, the various acts, operations, and / or functions shown can be executed in the order shown, executed in parallel, or in some cases omitted. Also, the order of processing is not necessarily required to implement the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the acts, operations, and / or functions shown can be repeatedly executed according to the particular strategy being used. Additionally, the acts, operations, and / or functions described can be represented graphically as code to be programmed into the non-transitory memory of a computer-readable storage medium for an engine control system, where the described acts are executed by executing instructions in a system including various engine hardware components in combination with an electronic controller.

[0096] It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments should not be considered in a limiting sense since numerous variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of various systems and configurations, as well as other features, functions, and / or characteristics disclosed herein.

[0097] The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims can refer to "one" element or "first" element, or their equivalents. These claims should be understood to include the combination of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics can be claimed by modifying these claims or presenting new claims in this application or a related application. Such claims, whether broader, narrower, the same, or different in scope from the original claims, are also regarded as included within the subject matter of the present disclosure.

[0098] According to the present invention, a method includes: in response to a surge indication after an accelerator pedal depression or release event, while maintaining the boost pressure at a certain level based on the torque demand, increasing the surge margin by adjusting each of the output of an electric motor coupled to a boosting device and the opening degree of a continuously variable compressor recycle valve (CCRV), and these adjustments are selected based on the torque demand after the accelerator pedal depression or release event.

[0099] According to one embodiment, the above invention is further characterized in that when the torque demand after the accelerator pedal depression or release is higher than a threshold demand, these adjustments include increasing the positive torque of the electric motor output while increasing the CCRV opening degree, and when the torque demand after the accelerator pedal depression or release is lower than the threshold demand, these adjustments include increasing the regenerative torque of the electric motor output while increasing the CCRV opening degree.

[0100] According to one embodiment, the above invention is further characterized in that when the torque demand is higher than the threshold demand, the engine operates with supercharging; and when the torque demand is lower than the threshold demand, the engine operates with natural aspiration.

[0101] According to one embodiment, the above invention is further characterized in that the adjustment of each of the electric motor output and the CCRV is also based on the state of charge of a battery coupled to the electric motor.

[0102] According to one embodiment, the above invention is further characterized in that when the torque demand after the accelerator pedal depression or release is lower than the threshold demand, the regenerative torque of the electric motor output increases by a greater amount as the state of charge of the battery decreases, and wherein the increase degree of the CCRV opening degree is adjusted based on increasing the regenerative torque of the electric motor output.

[0103] According to one embodiment, the above invention is further characterized in that when the torque demand after the accelerator pedal depression or release is higher than the threshold demand, the opening degree of the CCRV is based on the surge margin, and the positive torque of the electric motor output is based on a target boost pressure, which is based on the torque demand relative to the actual boost pressure and the adjusted CCRV opening degree, and wherein when the torque demand after the accelerator pedal depression or release is lower than the threshold demand, the opening degree of the CCRV is based on the surge margin, and the regenerative torque of the electric motor output is based on a target boost pressure, which is based on the torque demand relative to the actual boost pressure and the adjusted CCRV opening degree.

[0104] According to one embodiment, the opening degree of the CCRV increases as the surge margin decreases, wherein the positive torque output by the electric motor increases as the target boost pressure based on the torque demand exceeds the actual boost pressure when using the adjusted opening degree of the CCRV, and wherein the regenerative torque output by the electric motor increases as the actual boost pressure exceeds the target boost pressure based on the torque demand when using the adjusted opening degree of the CCRV.

[0105] According to one embodiment, the boosting device includes one of an electric supercharger and a turbocharger. When the boosting device is a turbocharger, the electric motor is coupled to one of the shaft of the turbocharger, the intake compressor, and the exhaust turbine. The opening degree of the compressor recirculation valve is increased to increase the air flow through the intake compressor of the turbocharger. The method further includes adjusting the position of the wastegate valve coupled to the exhaust turbine based on the torque demand after an accelerator pedal depression or release event.

[0106] According to one embodiment, when the torque demand after an accelerator pedal depression or release is higher than a threshold demand, the wastegate valve closes, and when the torque demand after an accelerator pedal depression or release is lower than the threshold demand, the wastegate valve opens.

[0107] According to the present invention, a method includes: in response to a first accelerator pedal release to a boosted engine operation, opening a continuously variable compressor recirculation valve (CCRV) by a first amount while increasing the power output by an electric motor coupled to the intake compressor of a turbocharger; and in response to a second accelerator pedal release to an unboosted engine operation, opening the CCRV by a second amount greater than the first amount while decreasing the power output by the electric motor.

[0108] According to one embodiment, increasing the power output by the electric motor includes providing positive motor torque from the electric motor to the compressor, and decreasing the power output by the electric motor includes providing regenerative motor torque from the electric motor to the compressor.

[0109] According to one embodiment, during the first accelerator pedal release, the first opening amount of the CCRV is based on the surge margin of the compressor, and the positive motor torque is based on the torque demand after the first accelerator pedal release. During the second accelerator pedal release, the second opening amount of the CCRV is based on the surge margin of the compressor, and the regenerative motor torque is based on the torque demand after the second accelerator pedal release.

[0110] According to one embodiment, during a first accelerator pedal release, a first quantity increases as the surge margin decreases, and positive motor torque increases as the target boost pressure based on torque demand after the first accelerator pedal release exceeds the actual boost pressure at a first quantity of CCRV opening; and wherein during a second accelerator pedal release, a second quantity increases as the surge margin decreases, and regenerative motor torque increases as the target boost pressure based on torque demand after the second accelerator pedal release drops below the actual boost pressure at a second quantity of opening.

[0111] According to one embodiment, during a first accelerator pedal release, the opening of the wastegate valve of the exhaust turbine coupled to the turbocharger is decreased, and the opening further decreases as the target boost pressure exceeds the actual boost pressure at a first quantity of CCRV opening, and wherein during a second accelerator pedal release, the opening of the wastegate valve is increased, and the opening further increases as the target boost pressure drops below the actual boost pressure at a second quantity of CCRV opening.

[0112] According to one embodiment, the features of the above invention further lie in that after each of the first accelerator pedal release and the second accelerator pedal release, when the actual boost pressure reaches the target boost pressure, the CCRV is closed and the electric motor is disabled.

[0113] According to one embodiment, in response to stepping on the accelerator pedal faster than a threshold to a boosted engine operation, the CCRV is opened while increasing the power of the electric motor output, the opening of the CCRV is based on the surge margin, and the power is increased.

[0114] According to the present invention, a vehicle system is provided, the vehicle system having: an engine; a turbocharger including an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor coupled to the shaft for providing electric assistance to the turbocharger; a wastegate including a wastegate actuator coupled across the exhaust turbine of the turbocharger; a compressor bypass including a continuously variable compressor recirculation valve (CCRV) coupled across the intake compressor of the turbocharger; a pressure sensor coupled to the intake system downstream of the compressor for estimating the pressure ratio across the compressor; and a controller having computer-readable instructions stored on a non-transitory memory for: estimating a surge limit margin of the compressor during a torque transient in response to an input from the pressure sensor; increasing the opening of the CCRV to increase the margin to exceed the threshold in response to the margin being less than the threshold; and adjusting the power output of the electric motor based on the difference between the actual boost pressure at the increased CCRV opening and the target boost pressure based on the torque transient.

[0115] According to one embodiment, the features of the above invention are further characterized in that when the torque transient includes a throttle pedal release event from boost to boost, the CCRV opening increases by a small amount, and the adjusted power output by the electric motor includes positive motor torque, where when the torque transient includes a throttle pedal release event from boost to non-boost, the CCRV opening increases by a large amount, and the adjusted power output by the electric motor includes regenerative motor torque.

[0116] According to one embodiment, when the torque transient includes a slow throttle pedal depression event, the CCRV opening increases by a small amount, and the adjusted power output by the electric motor includes a small amount of positive motor torque, and where when the torque transient includes a fast throttle pedal depression event, the CCRV opening increases by a large amount, and the adjusted power output by the electric motor includes a large amount of positive motor torque.

[0117] According to one embodiment, the controller includes additional instructions for: reducing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event or a throttle pedal depression event from boost to boost; and increasing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event from boost to non-boost.

Claims

1. A method for supercharging control of an engine, comprising: In response to a surge indication after an accelerator pedal depression event or an accelerator pedal release event, while maintaining the supercharging pressure at a certain level based on the torque demand, increasing the surge margin by adjusting each of the output of an electric motor coupled to a supercharging device and the opening degree of a continuously variable compressor recirculation valve (CCRV), the adjustment being selected based on the torque demand after the accelerator pedal depression event or the accelerator pedal release event.

2. The method according to claim 1, wherein when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is higher than a threshold demand, the adjustment includes increasing the positive torque of the electric motor output while increasing the opening degree of the CCRV, and when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is lower than the threshold demand, the adjustment includes increasing the regenerative torque of the electric motor output while increasing the opening degree of the CCRV.

3. The method according to claim 2, wherein when the torque demand is higher than the threshold demand, the engine operates in a supercharged mode, and when the torque demand is lower than the threshold demand, the engine operates in a naturally aspirated mode.

4. The method according to claim 2, wherein the adjustment of each of the output of the electric motor and the CCRV is further based on the state of charge of a battery coupled to the electric motor.

5. The method according to claim 4, wherein when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is lower than the threshold demand, the regenerative torque of the electric motor output increases by a greater amount as the state of charge of the battery decreases, and wherein the increase in the opening degree of the CCRV is adjusted based on the increase in the regenerative torque of the electric motor output.

6. The method according to claim 2, wherein when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is higher than the threshold demand, the opening degree of the CCRV is based on the surge margin, and the positive torque of the electric motor output is based on a target supercharging pressure, the target supercharging pressure being based on the torque demand relative to the actual supercharging pressure and the adjusted opening degree of the CCRV; and wherein when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is lower than the threshold demand, the opening degree of the CCRV is based on the surge margin, and the regenerative torque of the electric motor output is based on the target supercharging pressure, the target supercharging pressure being based on the torque demand relative to the actual supercharging pressure and the adjusted opening degree of the CCRV.

7. The method according to claim 6, wherein the opening degree of the CCRV increases as the surge margin decreases, wherein the positive torque output by the electric motor increases when the target boost pressure based on the torque demand exceeds the actual boost pressure in the case of using the adjusted opening degree of the CCRV, and wherein the regenerative torque output by the electric motor increases when the actual boost pressure exceeds the target boost pressure based on the torque demand in the case of using the adjusted opening degree of the CCRV.

8. The method according to claim 2, wherein the boosting device includes one of an electric supercharger and a turbocharger. When the boosting device is the turbocharger, the electric motor is coupled to one of the shaft of the turbocharger, the intake compressor, and the exhaust turbine. The opening degree of the compressor recirculation valve increases to increase the air flow through the intake compressor of the turbocharger. The method further includes adjusting the position of the wastegate valve coupled to the exhaust turbine based on the torque demand after the accelerator pedal depression event or the accelerator pedal release event.

9. The method according to claim 8, wherein the wastegate valve closes when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is higher than the threshold demand, and wherein the wastegate valve opens when the torque demand after the accelerator pedal depression event or the accelerator pedal release event is lower than the threshold demand.

10. A vehicle system, comprising: An engine; A turbocharger, the turbocharger including an intake compressor coupled to an exhaust turbine via a shaft, and an electric motor coupled to the shaft for providing electric assistance to the turbocharger; A wastegate, the wastegate including a wastegate actuator coupled across the exhaust turbine of the turbocharger; A compressor bypass, the compressor bypass including a continuously variable compressor recirculation valve (CCRV) coupled across the intake compressor of the turbocharger; A pressure sensor, the pressure sensor coupled to the intake system downstream of the compressor for estimating the pressure ratio across the compressor; And A controller having computer-readable instructions stored on a non-transitory memory, the instructions for: Estimating a surge limit margin of the compressor during a torque transient in response to an input from the pressure sensor; And In response to the margin being less than a threshold, Increasing the opening degree of the CCRV to increase the margin to exceed the threshold; And Adjusting the power output of the electric motor based on the difference between the actual boost pressure in the case of the increased opening degree of the CCRV and the target boost pressure based on the torque transient.

11. The system according to claim 10, wherein when the torque transient includes a throttle pedal release event from boost to boost, the CCRV opening increases by a smaller amount, and the adjusted power output by the electric motor includes positive motor torque, and wherein when the torque transient includes a throttle pedal release event from boost to no boost, the CCRV opening increases by a larger amount, and the adjusted power output by the electric motor includes regenerative motor torque.

12. The system according to claim 10, wherein when the torque transient includes a slower throttle pedal depression event, the CCRV opening increases by a smaller amount, and the adjusted power output by the electric motor includes a smaller amount of positive motor torque, and wherein when the torque transient includes a faster throttle pedal depression event, the CCRV opening increases by a larger amount, and the adjusted power output by the electric motor includes a larger amount of positive motor torque.

13. The system according to claim 10, wherein the controller includes additional instructions for: reducing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event or a throttle pedal depression event from boost to boost; and increasing the opening of the wastegate actuator when the torque transient includes a throttle pedal release event from boost to no boost.

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