Turbo speed control for mode transitions in a dual turbo system

A system for controlling an engine having a first turbocharger, a second turbocharger and a cutoff valve that regulates exhaust flow through a turbine of the second turbocharger, the system comprising: a speed determination module that determines a current speed of the first turbocharger, determines a current speed of the second turbocharger, and determines a target speed of the second turbocharger based on the current speed of the first turbocharger; and a boost control module that compares the target speed of the second turbocharger with the current speed of the second turbocharger, and that selectively adjusts a position of a cutoff valve to adjust the current speed of the second turbocharger based on the comparison.

FIELD

The present disclosure relates to dual turbo systems and more particularly to turbo speed control systems and methods in a dual turbo system.

BACKGROUND

Increasing fuel economy is a desirable goal for auto manufacturers. Consumers desire high fuel economy without sacrificing performance. Turbocharging provides a method for increasing performance during demanding conditions while reducing the overall fuel economy of the vehicle since a smaller displacement engine can be used.

One type of turbocharging system is a parallel turbocharger. In such a system, two turbines are provided in parallel and are capable of running simultaneously. In one mode of operation one turbine is spinning (on) while the other is not spinning (off). This mode will be referred to as single turbocharger mode. In another mode of operation both the turbines are spinning. This will be referred to as dual turbocharger mode. Providing a smooth transition between the modes is important for drivability of the vehicle.

SUMMARY

A system for controlling an engine is presented. The engine has a first turbocharger, a second turbocharger and a cutoff valve that regulates exhaust flow through a turbine of the second turbocharger. The system comprises a speed determination module and a boost control module. The speed determination module determines a current speed of the first turbocharger determines a current speed of the second turbocharger and determines a target speed of the second turbocharger based on the current speed of the first turbocharger. The boost control module compares the target speed of the second turbocharger with the current speed of the second turbocharger, and selectively adjusts a position of a cutoff valve to adjust the current speed of the second turbocharger based on the comparison.

DETAILED DESCRIPTION

An engine combusts air and fuel within cylinders to generate drive torque. Some engines are turbocharged engines that include a turbine which forces more air into the combustion chamber than atmospheric pressure alone. Some engines are dual turbo engines that have two separate turbochargers operating in either a sequence or in parallel. In a sequential turbocharged engine, a first turbine operates at low speeds and a second turbine starts operating at a higher speed and load (e.g. a predetermined engine speed and load).

A first sub-set of cylinders output exhaust to a first exhaust pipe and a second sub-set of cylinders output exhaust to a second exhaust pipe. A first turbine of a first turbocharger is connected to the first exhaust pipe and a second turbine of a second turbocharger is connected to the second exhaust pipe. Compressors of the first and second turbochargers provide compressed air to the engine.

A crossover pipe is connected upstream of the first and second turbines. A first bypass valve regulates exhaust bypassing the first turbine and a second bypass valve regulates exhaust bypassing the second turbine. A cutoff valve is connected downstream of the second turbine and regulates exhaust flow through the second turbine and the second bypass valve.

Most parallel-turbocharged engines have two modes of operation: a single turbocharger mode and a dual turbocharger mode. In the single turbocharger mode, only one of the two turbochargers is active. For example, a cutoff valve located downstream of the turbine of the second turbocharger may be at least partially closed and/or the second compressor bypass valve may be at least partially open in the single turbocharger mode. In a dual turbocharger mode, both of the turbochargers are active.

Switching between the single turbocharger mode and the dual turbocharger mode abruptly can lead to a sudden jump and/or drop in the torque provided by the engine. Abrupt switches between the two modes can lead to a noticeable degradation in the drivability of the vehicle thereby providing a poor driving experience. For example, a sudden increase or decrease in torque can result in a jerk being felt by the driver and the passengers of the vehicle. The present disclosure provides methods and systems for smoothing the transition between the modes. Consequently, the switch between the modes is less noticeable, thereby increasing the drivability of the vehicle and providing an enhanced driving experience.

Referring now toFIG. 1, a functional block diagram of an example engine and exhaust system100is presented. The system100includes an engine102and an engine control module (ECM)104. The engine control module (ECM)104controls the engine102that combusts an air/fuel mixture to produce drive torque for a vehicle. The ECM104controls the engine102based on driver input received from a driver input module108. Air is drawn into the engine102through an intake system112. For example only, the intake system112may include an intake manifold116and a throttle valve120. For example only, the throttle valve120may include a butterfly valve having a rotatable blade. The ECM104controls an opening of the throttle valve120to control the amount of air drawn into the intake manifold116.

Air from the intake manifold116is drawn into cylinders (not shown) of the engine102. The engine102may include multiple cylinders. For example only, the engine102may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. Under some circumstances, the ECM104may selectively deactivate one or more of the cylinders, which may improve fuel economy under certain engine operating conditions.

The engine102may operate using a four-stroke cycle. The four strokes are named the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke. During each revolution of a crankshaft (not shown), two of the four strokes occur within the cylinder. Therefore, two crankshaft revolutions are necessary for the cylinder to experience all four of the strokes.

The injected fuel mixes with air and creates an air/fuel mixture in the cylinder. During the compression stroke, a piston (not shown) within the cylinder compresses the air/fuel mixture. The engine102may be a compression-ignition engine, in which case compression in the cylinder ignites the air/fuel mixture. Alternatively, the engine102may be a spark-ignition engine, in which case a signal from the ECM104energizes a spark plug in the cylinder, which ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as top dead center (TDC).

The timing of the spark may be controlled by a timing signal specifying how far before or after TDC to generate the spark. Because piston position is directly related to crankshaft rotation, spark timing may be synchronized with the crankshaft angle. In various implementations, spark to deactivated cylinders may be halted.

The engine102may have two banks of cylinders. A first bank124of cylinders of the engine102outputs exhaust to a first exhaust manifold136. A second bank128of cylinders of the engine102outputs exhaust to a second exhaust manifold140.

The first exhaust manifold136outputs the exhaust from the first bank124of cylinders to a first exhaust pipe144. The second exhaust manifold140outputs the exhaust from the second bank128of cylinders to a second exhaust pipe148. A crossover pipe152is connected between the first and second exhaust pipes144and148. Exhaust can flow from the first exhaust pipe144to the second exhaust pipe148through the crossover pipe152and vice versa.

The system100includes first and second turbochargers that provide pressurized air to the intake manifold116. The first and second turbochargers may be single scroll turbochargers. The first turbocharger includes a first turbine156and a first compressor160. The second turbocharger includes a second turbine164and a second compressor168. Exhaust flow through the first turbine156drives the first turbine156, and exhaust flow through the second turbine164drives the second turbine164. A first turbine bypass valve172(or wastegate) may enable exhaust to bypass the first turbine156. A second turbine bypass valve176(or wastegate) may enable exhaust to bypass the second turbine164.

The first and second turbines156and164are located downstream of the locations where the crossover pipe152joins the first and second exhaust pipes144and148. In other words, the crossover pipe152is connected between the first and second exhaust pipes144and148upstream of the first and second turbines156and164.

The first turbine156is mechanically coupled to the first compressor160, and the first turbine156drives rotation of the first compressor160. The first compressor160provides compressed air to the throttle valve120. A first compressor bypass valve180may enable air to bypass the first compressor160. The second turbine164is mechanically coupled to the second compressor168, and the second turbine164drives rotation of the second compressor168. The second compressor168also provides compressed air to the throttle valve120. A second compressor bypass valve184may enable air to bypass the second compressor168. The first and second compressors160and168, the first and second compressor bypass valves180and184, and associated tubing is collectively illustrated by188. In various implementations, a MAF sensor192may be located upstream of the first and second compressors160and168. Additionally, one MAF sensor may be provided for each bank of cylinders.

A cutoff valve196is actuatable to vary exhaust flow through the cutoff valve196. When the cutoff valve196is actuated to cut off exhaust flow, the exhaust from the second bank of cylinders is directed to the first exhaust pipe144through the crossover pipe152. The cutoff valve196may be actuated to cut off exhaust flow, for example, to reduce or prevent exhaust flow through the second turbine164. Reducing exhaust flow through the second turbine164reduces the output of the second compressor168.

The ECM104may control boost (e.g., amount of intake air compression) provided by the first and/or second turbochargers via a boost actuator module200. More specifically, the ECM104may control the cutoff valve196, the first and second turbine bypass valves172and176, and/or the first and second compressor bypass valves180and184via the boost actuator module200. For example, the boost actuator module200may control duty cycle or position of the first turbine bypass valve172, the second turbine bypass valve176, the first compressor bypass valve180, the second compressor bypass valve184, and the cutoff valve196to control boost provided by the first and second turbochargers.

The system100may also include an exhaust gas recirculation (EGR) valve204that selectively redirects exhaust gas back to the intake manifold116. An EGR actuator module208may control the EGR valve204based on signals from the ECM104.

A pressure within the intake manifold116may be measured using a manifold absolute pressure (MAP) sensor212. In various implementations, engine vacuum, which may refer to a difference between ambient air pressure and the pressure within the intake manifold116, may be measured. A mass flow rate of air flowing into the intake manifold116may be measured using a mass air flow (MAF) sensor192. In various implementations, the MAF sensor192may be located in a housing that also includes the throttle valve120.

An ambient temperature of air being drawn into the engine102may be measured using an intake air temperature (IAT) sensor216. A pressure within the cylinder may be measured using a cylinder pressure sensor. A cylinder pressure sensor may be provided for each cylinder. The ECM104may use signals from the sensors to make control decisions for the engine system.

The ECM104may communicate with a transmission control module220to coordinate shifting gears in a transmission (not shown). For example, the ECM104may reduce engine torque during a gear shift. The ECM104may communicate with a hybrid control module to coordinate operation of the engine102and an electric motor.

A manifold absolute pressure (MAP) sensor or a mass air flow (MAF) sensor may be placed at the inlet of the first compressor160and/or the second compressor168to measure the inlet pressure of the first compressor160and/or the second compressor168, respectively. Another MAP or MAF sensor may be placed at the outlet of the first compressor160and/or the second compressor168to measure an outlet pressure of the first compressor160and/or the second compressor168, respectively. The MAF sensors may be used to measure an amount of mass air flow provided by the first turbocharger and/or the second turbocharger.

The ECM104is configured to facilitate a smoother transition between the single turbocharger mode and the dual turbocharger mode according to the principles of the present disclosure, as described below.

Referring now toFIG. 2, a functional block diagram of an example implementation of the ECM104is presented. A load request module224may determine a load request228based on one or more driver inputs232, such as an accelerator pedal position, a brake pedal position, a cruise control input, and/or one or more other suitable driver inputs. The load request module224may determine the load request228additionally or alternatively based on one or more other load requests, such as torque requests generated by the ECM104and/or torque requests received from other modules of the vehicle, such as the transmission control module220, the hybrid control module, a chassis control module, etc. One or more engine actuators may be controlled based on the load request228and/or one or more other vehicle operating parameters.

For example, a throttle control module236may determine a target throttle opening240based on the load request228. A throttle actuator module244may adjust opening of the throttle valve120based on the target throttle opening240. A spark control module248may determine a target spark timing252based on the load request228. A spark actuator module256may generate spark based on the target spark timing252.

A fuel control module260may determine one or more target fueling parameters264based on the load request228. For example, the target fueling parameters264may include number of fuel injection pulses (per combustion event), timing for each pulse, and amount for each pulse. A fuel actuator module268may inject fuel based on the target fueling parameters264.

A cylinder control module272may determine a target number of cylinders to deactivate and/or deactivate276based on the load request228. A cylinder actuator module280may activate and deactivate cylinders of the engine102based on the target number276. An EGR control module284may determine a target EGR opening288for the EGR valve204based on the load request228. The EGR actuator module208may control the EGR valve204based on the target EGR opening288.

A phaser control module292may determine target phaser positions296for intake and exhaust camshafts. A phaser actuator module300controls phasing of the intake and exhaust camshafts via intake and exhaust cam phasers based on the target phaser positions296.

A boost control module304may determine a target boost308based on the load request228. The boost actuator module200may control the cutoff valve196based on the target boost308. The boost actuator module200may, for example, determine a target position for the cutoff valve196based on the target boost308and control the cutoff valve196based on the target position. Additionally or alternatively, the boost actuator module200may determine a target duty cycle based on the target boost308and apply a pulse width modulation (PWM) signal to the cutoff valve196based on the target duty cycle. The boost actuator module200may additionally or alternatively determine target positions for the first and second turbine bypass valves172and176based on the target boost308and control the first and second turbine bypass valves172and176based on the target positions, respectively. When the cutoff valve196is closed, the boost actuator module200may open the second compressor bypass valve184.

In various implementations, the cutoff valve196may be a two-position device, and the boost actuator module200may determine whether to open the cutoff valve196to a predetermined open position or to close the cutoff valve196to a predetermined closed position based on the target boost308. The boost actuator module200may open the cutoff valve196to the predetermined open position or close the cutoff valve196to the predetermined closed position based on the determination.

A target speed determination module312may determine a target speed316for the second turbine164(i.e. the second turbocharger) using an engine parameter320. The engine parameter320may include a first value representing a first current speed of the first turbine156and an estimated speed of the first turbine156and the second turbine164in dual turbocharger mode. The engine parameter320may include value(s) representing one or more of an inlet pressure of the first compressor160, an outlet pressure of the first compressor160, an inlet pressure of the second compressor168and an outlet pressure of the second compressor168. The engine parameter320may also include a value representing a position of one or more of the first turbine bypass valve172, the first compressor bypass valve180, the second turbine bypass valve176, the second compressor bypass valve184and the cutoff valve196. The engine parameter320may also include an engine speed, for example in revolutions per minute (RPM), that may be generated based on the position of the crankshaft.

In an alternative embodiment, the target speed determination module312may compute a first difference between the estimated speed of the first turbocharger in dual turbocharger mode and the speed of the first turbocharger in single turbocharger mode (i.e. speed of the first turbine156). Then the target speed determination module312may select a target speed316for the second turbocharger such that a second difference between the target speed316and the estimated speed of the first turbocharger in dual turbocharger mode is equal to the first difference.

In another alternative embodiment, the target speed determination module312may select a target speed316for the second turbocharger such that the values of compressor inlet pressure and/or the compressor outlet pressure for the first compressor160and/or the second compressor168remain within certain predefined ranges and do not go below the lower bound limit of the range or above the upper bound limit of the range. The target speed determination module312may determine the target speed316for the second turbocharger using a lookup table that specifies specific target speeds based on the compressor inlet and/or the compressor outlet pressure.

In another alternative embodiment, the target speed determination module312may determine the target speed316using a lookup table that specifies the target speed316based on the speed of the first turbocharger (i.e., the speed of the first turbine156), the estimated speed of the first and second turbochargers in dual turbocharger mode (i.e., the estimated speed of the first turbine156and the second turbine164), and/or any other engine parameter320.

The target speed determination module312provides the target speed316to the boost control module304. The boost control module304compares the target speed316of the second turbocharger with a current speed of the second turbocharger. If the current speed of the second turbocharger is equal to the target speed316, then the boost control module304maintains the current position of the cutoff valve196, the first turbine bypass valve172and the second turbine bypass valve176.

If the current speed of the second turbocharger is less than the target speed316, then the boost control module304opens the cutoff valve196to increase the speed of the second turbocharger. Opening the cutoff valve196allows more exhaust to flow through the second turbine164which increases the speed of the second turbocharger. The boost control module304may close the first turbine bypass valve172and/or the second turbine bypass valve176to keep exhaust gas flow through the first turbine156unchanged. When the exhaust gas flow through the first turbine156is unchanged, the speed of the first turbine156remains unchanged and the first compressor160compresses and feeds the same amount of air into the engine102resulting in an unchanged boost.

If the current speed of the second turbocharger is greater than the target speed316, then the boost control module304closes the cutoff valve196to decrease the speed of the second turbocharger. Closing the cutoff valve196decreases the amount of exhaust that flows through the second turbine164which decreases the speed of the second turbocharger. The boost control module304may open the first turbine bypass valve172and/or the second turbine bypass valve176to keep exhaust gas flow through the first turbine156unchanged. When the exhaust gas flow through the first turbine156is unchanged, the speed of the first turbine156remains unchanged and the first compressor160compresses and feeds the same amount of air into the engine102resulting in an unchanged boost.

The boost control module304may close the second compressor bypass valve184when the current speed of the second turbocharger is less than the target speed316in order to increase the speed of the second turbocharger. Closing the second compressor bypass valve184decreases the load on the second compressor168.

The boost control module304may control a position of the first turbine bypass valve172and/or the second turbine bypass valve176to achieve a target boost. The boost control module304compares a current boost with the target boost.

If the current boost is less than the target boost, then the boost control module304closes the first turbine bypass valve172. Closing the first turbine bypass valve172forces more exhaust to go through the first turbine156causing the first turbine156to spin faster. A faster spinning first turbine156causes the first compressor160to compress more air and feed more compressed air into the engine102. More compressed air being fed into the engine102results in more boost. The boost control module304may close the second turbine bypass valve176and/or the cutoff valve196to further increase the boost.

If the current boost is greater than the target boost, then the boost control module304opens the first turbine bypass valve172. Opening the first turbine bypass valve172allows exhaust to bypass the first turbine156causing the first turbine156to spin slower. A slower spinning first turbine156causes the first compressor160to compress less air and feed less compressed air into the engine102. Less compressed air being fed into the engine102results in a lesser boost. The boost control module304may open the second turbine bypass valve176and/or the cutoff valve196to further decrease the boost.

Referring now toFIG. 3, an example method350for controlling the speed of a turbocharger in a dual turbo system begins at352.

At354, the method350determines a first current speed of the first turbocharger. The first current speed of the first turbocharger may be determined by using a sensor to measure the current speed at which the first turbine156is rotating. Alternatively, the sensor may measure the current speed at which the first compressor160is rotating or the speed at which a shaft connected with the first turbine156is rotating. Alternatively, the first current speed of the first turbocharger may be estimated, for example, based on the pressure across and air flow through the first compressor160and/or any other engine parameter320. A lookup table may be used to determine the current speed of the first turbocharger based on a known pressure across and air flow through the first compressor160and/or any other engine parameter320.

At358, the method350determines a target speed316of the second turbocharger based on the first current speed of the first turbocharger. The target speed316may be determined in any of the ways described above.

At362, the method350determines a second current speed of the second turbocharger. The second current speed of the second turbocharger may be measured or estimated, similar to the manner in which the first current speed of the first turbocharger is determined, as described above.

At366, the method350compares the target speed316of the second turbocharger with the second current speed of the second turbocharger. For example, the boost control module304determines whether the second current speed is less than the target speed316of the second turbocharger.

If the second current speed is less than the target speed316of the second turbocharger, then, at370, the method350opens a cutoff valve196to increase the second turbocharger speed. At374, the method350closes the second compressor bypass valve184to further increase the second turbocharger speed.

If, however, the second current speed is not less than the target speed316of the second turbocharger, then, at378, the method350determines whether the second current speed is greater than the target speed316of the second turbocharger.

If the second current speed is greater than the target speed316of the second turbocharger, then, at382, the method350closes the cutoff valve196to decrease the second current speed of the second turbocharger.

If the second current speed of the second turbocharger is neither greater nor less than the target speed316of the second turbocharger, then the current speed of the second turbocharger must be equal to the target speed316of the second turbocharger. In this scenario, the method350maintains the position of the cutoff valve196, at386, in order to maintain the speed of the second turbocharger.

At390, the method350controls a position of the first turbine bypass valve172and/or the second turbine bypass valve176to achieve a target boost. The method350ends at394.

Referring now toFIG. 4, another example method400of controlling the speed of a turbocharger in a dual turbo system begins at402.

At404, the method400receives a load request228, for example from the load request module224. The load request228specifies a value indicating an amount of torque requested based on a driver input.

At408, the method400determines whether the engine102is to be operated in the dual turbocharger mode or the single turbocharger mode in order to produce the requested torque. If the requested torque exceeds the engine torque capacity in single turbocharger mode, then the engine102is to be operated in the dual turbocharger mode. However, if the requested torque can be produced by the engine with only the first turbocharger being active, then the engine102is to be operated in the single turbocharger mode.

At412, the method400determines whether the engine102is being switched from the dual turbocharger mode to the single turbocharger mode. The method400may determine the current mode of operation of the engine102by determining whether the second turbocharger is active. If the second turbocharger is active then the engine102is operating in the dual turbocharger mode.

If the engine102is to be switched from the dual turbocharger mode to the single turbocharger mode, then, at416, the method400creates a discrepancy between the speeds of the first and second turbochargers.

The method400may create the speed discrepancy between the first and second turbochargers by increasing the speed of the first turbocharger. The method400increases the speed of the first turbocharger, so that the first turbocharger is closer to the speed at which the first turbocharger will operate in the single turbocharger mode. The method400may increase the speed of the first turbocharger mode by closing the cutoff valve196.

In an alternative embodiment, the method400may create the speed discrepancy between the first and second turbochargers by decreasing the speed of the second turbocharger. The method400decreases the speed of the second turbocharger, so that the second turbocharger is closer to a speed of zero. The method400may decrease the speed of the second turbocharger by closing the cutoff valve196.

While the engine102is being switched from the dual turbocharger mode to the single turbocharger mode, the method400maintains the second compressor bypass valve184in a closed position, at420. The second compressor bypass valve184is maintained in the closed position, so that the second compressor168can continue to supply air to the engine102. Advantageously, by holding the second compressor bypass valve184closed, more energy is extracted from the second turbocharger while the first turbocharger is ramping up.

The method400determines whether spark is needed to adjust the torque during the switch from the dual turbocharger mode to the single turbocharger mode. If spark is needed during the switch then, the method400provides spark in order to fulfill the requested torque, at424. The method400creates a spark reserve in advance to compensate for a potential spark advance capability loss due to an increase in the engine backpressure in the single turbocharger mode.

If the engine102is not being switched from the dual turbocharger mode to the single turbocharger mode, then the method400determines whether the engine is being switched from the single turbocharger mode to the dual turbocharger mode, at428.

If the engine102is being switched from the single turbocharger mode to the dual turbocharger mode, the method400maintains the current position of the first turbine bypass valve172or closes the first turbine bypass valve172and opens the cutoff valve196during the switch, at432. The first turbine bypass valve172is maintained in the current position or continues to be closed until the second turbocharger is ramped up. Once the second turbocharger is up to speed, the method400may open the first turbine bypass valve172to maintain the speed of or slow down the first turbocharger.

At436, the method400determines whether spark is needed to adjust the torque during the switch. If spark is needed, then the method400uses spark to adjust the torque, so that the output torque is equal to the requested torque.

The method400compares the output torque of the engine102with the requested torque. If the output torque is less than the requested torque, then the method400uses spark advance to increase the output torque of the engine102. If the output torque is greater than the requested torque, then the method400uses spark retard to decrease the output torque of the engine102. The method400ends at440.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared processor encompasses a single processor that executes some or all code from multiple modules. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more modules. The term shared memory encompasses a single memory that stores some or all code from multiple modules. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more modules. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage.