Turbocharger control

Various systems and methods for controlling a turbocharger of an engine via a wastegate are described. In one example, the wastegate is adjusted according to a difference between the boost pressure and the atmospheric pressure. In this manner, the interdependency between controlling the boost pressure and using the boost pressure to actuate the wastegate in a boost-based wastegate configuration may be reduced.

FIELD

The present application relates to systems for controlling a turbocharger of an engine with a wastegate.

BACKGROUND AND SUMMARY

Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to the exhaust manifold side and the compressor is coupled to the intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, such as with a wastegate.

In one example, the wastegate may include a first port coupled to boost pressure, a second port coupled to atmospheric pressure, and a valve configured to control the flow of exhaust gasses according to the wastegate duty cycle. This configuration may be referred to as a “boost-based” configuration because the force to actuate the wastegate valve comes from the boost pressure. For example, a solenoid valve may connect a wastegate canister chamber having a wastegate canister pressure to the first port coupled to boost pressure and the second port coupled to atmospheric pressure. When the solenoid valve is in a first position, the first port and the wastegate canister chamber are in communication and the wastegate canister pressure will increase toward boost pressure. When the solenoid valve is in a second position, the second port and the wastegate canister chamber are in communication and the wastegate canister pressure will decrease toward atmospheric pressure. By moving the solenoid valve from the first position to the second position via the wastegate (solenoid) duty cycle, the wastegate canister pressure may be maintained at a value between the boost pressure and the atmospheric pressure. The wastegate canister pressure may be used to actuate the wastegate valve and thus control the boost pressure. Thus, the position of the wastegate valve may be determined by the boost pressure, atmospheric pressure, and the wastegate duty cycle.

The inventors herein have recognized that the wastegate is used to control the boost pressure, and the boost pressure relative to atmospheric pressure provides the motive force for moving the wastegate. For example, the atmospheric pressure may change with altitude or weather conditions which may affect the pressure difference between boost and atmospheric pressure, and hence the ability to control the boost pressure. Additionally, a circular interaction of controlling the boost pressure with the wastegate and actuating the wastegate with the boost pressure makes the wastegate operation less predictable than desired. One approach to address the above issues is a method that includes actuating the wastegate with boost pressure generated by the turbocharger. The wastegate is adjusted according to a difference between the boost pressure and the atmospheric pressure. In this way, the interdependency between controlling the boost pressure and using the boost pressure to actuate a boost-based wastegate is reduced.

DETAILED DESCRIPTION

The following description relates to systems for controlling turbochargers of internal combustion engines via a wastegate. An example embodiment of an engine with a turbocharger including a wastegate is illustrated inFIG. 1. In the example configuration, the force for actuating the wastegate is provided by the boost pressure. The example wastegate is shown in more detail inFIG. 2. The example wastegate comprises a solenoid valve and a wastegate canister. InFIGS. 3 and 4, the solenoid valve is shown in two positions to illustrate how the solenoid valve may be used to control the pressure of the wastegate canister.FIG. 5illustrates prophetic data of wastegate canister pressure when the solenoid valve is modulated as described inFIGS. 3 and 4. A force generated by the wastegate canister pressure may be used to actuate the wastegate valve to control the turbocharger. The wastegate ofFIG. 2may be adjusted using a control routine, such as illustrated inFIGS. 6 and 7, for controlling the turbocharger. In this manner, the physical interaction between controlling the boost pressure and using the boost pressure to actuate the wastegate may be reduced in a turbocharger system that uses boost pressure for actuating the wastegate.

FIG. 1shows an example of a turbocharged engine including a wastegate. Internal combustion engine10comprises a plurality of cylinders, one cylinder of which is shown inFIG. 1. Engine10may receive control parameters from a control system including controller12and input from a vehicle operator130via an input device132. In this example, input device132includes an accelerator pedal and a pedal position sensor134for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber”)14of engine10may include combustion chamber walls136with piston138positioned therein. Piston138may be coupled to crankshaft140so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft140may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to crankshaft140via a flywheel to enable a starting operation of engine10.

Cylinder14can receive intake air via a series of intake air passages142,144, and146. Intake air passage146can communicate with other cylinders of engine10in addition to cylinder14. In some embodiments, one or more of the intake passages may include a turbocharger boosting device. For example, engine10is configured with a turbocharger including a compressor174arranged between intake passages142and144, and an exhaust turbine176arranged between exhaust passages148and149. Specifically, air passage142is connected to the compressor inlet, air passage144is connected to the compressor outlet, exhaust passage148is connected to the turbine inlet, and exhaust passage149is connected to the turbine outlet. Compressor174may be at least partially powered by exhaust turbine176via a shaft180. Wastegate177includes a path for exhaust gasses to flow from exhaust passage148away from turbine176to exhaust passage149. The energy supplied by turbine176may be controlled by controlling the amount of exhaust gas reaching turbine176from exhaust passage148. Specifically, the boost pressure may be adjusted by the WGC signal received from controller12by modulating a degree of opening, and/or a duration of opening, of a wastegate valve.

In the example embodiment, wastegate177is pneumatically actuated to control the wastegate valve and hence the boost pressure. In what is known as a “boost-based” wastegate configuration, wastegate177comprises a solenoid valve including a first port (not shown) connected to intake passage146and a second port (not shown) connected to an intake passage at atmospheric pressure, such as intake passage142. The pressure of the first port is at the boost pressure and may be measured with sensor125. The measurement may be sent to controller12via the TIP signal. Atmospheric pressure may be measured by sensor123and the measurement may be transmitted to controller12via the PA signal. In the example embodiment, the wastegate valve is normally closed, but force supplied by the boost pressure may be used to open the wastegate valve.

A throttle162including a throttle plate164may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle162may be disposed downstream of compressor174as shown inFIG. 1, or alternatively may be provided upstream of compressor174.

Exhaust passage148can receive exhaust gases from other cylinders of engine10in addition to cylinder14. Exhaust gas sensor128is shown coupled to exhaust passage148upstream of turbine176and emission control device178. Sensor128may be selected from among various suitable sensors for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a NOx, HC, or CO sensor, for example. Emission control device178may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.

Exhaust temperature may be measured by one or more temperature sensors (not shown) located in exhaust passages148and149. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhaust temperature may be computed by one or more exhaust gas sensors128. It may be appreciated that the exhaust gas temperature may alternatively be estimated by any combination of temperature estimation methods listed herein.

Each cylinder of engine10may include one or more intake valves and one or more exhaust valves. For example, cylinder14is shown including at least one intake poppet valve150and at least one exhaust poppet valve156located at an upper region of cylinder14. In some embodiments, each cylinder of engine10, including cylinder14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder. The opening and closing of the valves may be controlled by hydraulically actuated lifters coupled to valve pushrods, or via a cam profile switching mechanism. For example, intake valve150and exhaust valve156may be controlled by cam actuation via respective cam actuation systems151and153. Cam actuation systems151and153may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller12to vary valve operation. The position of intake valve150and exhaust valve156may be determined by valve position sensors155and157, respectively. In alternative embodiments, the intake and/or exhaust valve may be controlled by electric valve actuation. For example, cylinder14may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. In one specific example, twin independent variable cam timing may be used, where each of the intake cam and the exhaust cam can be independently adjusted by the control system.

In some embodiments, each cylinder of engine10may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder14is shown including one fuel injector166. Fuel injector166is shown coupled directly to cylinder14for injecting fuel directly therein in proportion to the pulse width of signal FPW-1 received from controller12via electronic driver168. In this manner, fuel injector166provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into combustion cylinder14. WhileFIG. 1shows injector166as a side injector, it may also be located overhead of the piston, such as near the position of spark plug192. Such a position may improve mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing. Fuel may be delivered to fuel injector166from a high pressure fuel system8including fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel may be delivered by a single stage fuel pump at lower pressure, in which case the timing of the direct fuel injection may be more limited during the compression stroke than if a high pressure fuel system is used. Further, while not shown, the fuel tanks may have a pressure transducer providing a signal to controller12. It will be appreciated that, in an alternate embodiment, injector166may be a port injector providing fuel into the intake port upstream of cylinder14.

Controller12is shown inFIG. 1as a microcomputer, including microprocessor unit106, input/output ports108, an electronic storage medium for executable programs and calibration values shown as read only memory (ROM) chip110in this particular example, random access memory (RAM)112, keep alive memory (KAM)114, and a data bus. Storage medium read-only memory110can be programmed with computer readable data representing instructions executable by processor102for performing the methods described below as well as other variants that are anticipated but not specifically listed. Controller12may receive various signals from sensors coupled to engine10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor122; engine coolant temperature (ECT) from temperature sensor116coupled to cooling sleeve118; a profile ignition pickup signal (PIP) from Hall effect sensor120(or other type) coupled to crankshaft140; throttle position (TP) from a throttle position sensor; throttle inlet pressure (TIP) from sensor125, and absolute manifold air pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller12from signal PIP. Further, crankshaft position, as well as crankshaft acceleration, and crankshaft oscillations may also be identified based on the signal PIP. Manifold air pressure signal MAP from manifold pressure sensor124may be used to provide an indication of vacuum, or pressure, in the intake manifold. Further, manifold pressure may be estimated based on other operating parameters, such as based on MAF and RPM, for example.

Continuing now withFIG. 2, a schematic of an example embodiment of wastegate177including solenoid valve200, wastegate canister230, wastegate arm240and mechanical linkages250is illustrated. Mechanical linkages250may convert the translational motion of mechanical arm240into a rotational motion of the wastegate valve. In other words, by moving mechanical arm along direction260, the wastegate valve may open or close so that exhaust gasses may be directed away from or toward turbine176, respectively. Wastegate arm240is attached to diaphragm232such that when a pressure difference is created across diaphragm232, it may force wastegate arm240away from its default position and open the wastegate valve. Spring234, attached to wastegate arm240, forces wastegate arm240toward its default position. In the example embodiment, the default position of wastegate arm240closes the wastegate valve.

The position of the wastegate valve is determined by the pressure inside canister volume236which is determined by the flow of gasses between solenoid valve200and canister volume236via connecting tube220. Gas flow is determined by the position of shuttle208and the pressures at first port202, second port204, and control port206. Shuttle208may move along direction214as determined by the forces from coil212and spring210. In the example embodiment, first port202is connected to intake passage146at boost pressure, second port204is connected to intake passage142at atmospheric pressure, and control port206is connected to canister volume236at canister pressure.

InFIG. 2, shuttle208is blocking control port206so gasses are substantially prevented from flowing between solenoid valve200and wastegate canister230. In the example embodiment, the position of shuttle208inFIG. 2may be in a transient position.FIG. 3illustrates the position of shuttle208in a steady-state position when coil212is discharged, such as when the WGC signal is driven low. When the coil is discharged, the force of spring210acting on shuttle208may hold shuttle208near spring210in solenoid valve200. In this position, port204is blocked by shuttle208and a channel is open between ports202and206. When the boost pressure exceeds the canister pressure, gasses may flow from port202to206as shown by arrows300, and the canister pressure may be increased.

FIG. 4illustrates shuttle208in a steady-state position when coil212is charged, such as when the WGC signal is driven high. When the coil is charged, the force of coil212may exceed the force of spring210acting on shuttle208so shuttle208may be positioned near coil212in solenoid valve200. In this position, port202is blocked by shuttle208and a channel is open between ports204and206. When the canister pressure exceeds the atmospheric pressure, gasses may flow from port206to204as shown by arrows400, and the canister pressure may be decreased.

Pulse width modulation (PWM) may be used to drive the WGC signal connected to coil212. A PWM signal may alternate between a high value and a low value at a given frequency and a duty cycle, where the duty cycle is defined as the proportion of time the signal is high divided by the period of the signal. In this manner, shuttle208may be actuated in a first direction (opening the channel between ports204and206) when the WGC signal is high and shuttle208may be actuated in a second direction opposite the first direction (opening the channel between ports202and206) when the WGC signal is low. By controlling the duty cycle of the WGC signal, an intermediate canister pressure between the boost pressure and atmospheric pressure may be maintained in canister volume236. The prophetic data ofFIG. 5illustrates how a PWM signal may be used to control the wastegate canister pressure. InFIG. 5, the intermediate canister pressure may be obtained by modulating the WGC signal at approximately 32 Hz. The PWM period can be measured as the time between peaks510or valleys520of the canister pressure. In alternative embodiments, the PWM frequency may be less than 200 Hz.

The average canister pressure may be increased by increasing the duration that ports202and206are in communication, such as when the WGC signal is low and coil212is discharged. In this manner, the canister pressure may be increased toward the boost pressure. The average canister pressure may be decreased by increasing the duration that ports204and206are in communication, such as when the WGC signal is high and coil212is charged. In this manner, the canister pressure may be decreased toward atmospheric pressure. Thus, the canister pressure may be adjusted by adjusting the duty cycle of the WGC signal. Specifically, the canister pressure may be increased by decreasing the duty cycle of the WGC signal and the canister pressure may be decreased by increasing the duty cycle of the WGC signal.

The canister pressure may be determined by the duty cycle of the WGC signal, the boost pressure, and the atmospheric pressure. For different atmospheric pressures, a given wastegate command may change the canister pressure by different amounts. For example, at high altitudes with lower atmospheric pressure, a difference between the boost pressure and the atmospheric pressure is greater than at low altitudes with higher atmospheric pressure. As the difference between the boost pressure and the atmospheric pressure increases, the canister pressure may be changed more rapidly. Thus, a wastegate command may be adjusted according to atmospheric pressure. For example, as atmospheric pressure increases, the wastegate command may be adjusted to increase actuation of the wastegate. As atmospheric pressure decreases, the wastegate command may be adjusted to decrease actuation of the wastegate. Similarly for different boost pressures, the wastegate command changes the canister pressure by different amounts. For example, as the boost level increases, the canister pressure may change more rapidly and the wastegate duty cycle may be adjusted to reduce the actuation of the wastegate.

The canister pressure may determine the degree that the wastegate valve is open or closed which determines the energy produced by the turbine and hence the boost. Since the boost pressure is the controlled variable and also the source for powering the wastegate, a control method that decouples the interaction between powering the wastegate and controlling the boost is desirable.

As further elaborated with reference toFIG. 6, a method600may be executed by an engine controller, such as12, for controlling the turbocharger via boost-based wastegate177. In one example, a method of controlling a turbocharger of an engine via a wastegate may comprise determining an atmospheric pressure and an actual boost pressure. The wastegate may be adjusted according to a difference between the actual boost pressure and the atmospheric pressure.

Continuing withFIG. 6, at610, the method includes determining a desired boost according to engine operating conditions. The conditions assessed may be directly measured with sensors, such as sensors116,120,122,123, and128for example, and/or the conditions may be estimated from other engine operating conditions. The assessed conditions may include engine oil temperature, engine speed, idle speed, barometric pressure, a driver-demanded torque (for example, from a pedal-position sensor), manifold air flow (MAF), air temperature, vehicle speed, etc.

Next, at620, an actual boost may be determined. The actual boost may be directly measured from a sensor, such as sensor125. The measurement may be sent to controller12via the TIP signal and stored in a computer readable storage medium. In an alternative embodiment, the actual boost may be estimated based on other operating parameters, such as based on MAP and RPM, for example.

Next, at630, atmospheric pressure may be determined. For example, atmospheric pressure may be measured near the compressor inlet, such as with sensor123. The measurement may be sent to controller12via the PA signal and stored in a computer readable storage medium. In an alternative embodiment, the atmospheric pressure may be estimated based on other operating parameters.

Next, at640, a wastegate actuation force may be calculated from a difference between the actual boost and atmospheric pressure. The wastegate may be adjusted according to the wastegate actuation force. Since the wastegate actuation force may accurately resemble the pressure differential between first port202and second port204of solenoid valve200, the interaction between powering wastegate177and controlling the boost may be reduced. For example, the wastegate actuation force may be used as an input to an inverse wastegate model. The inverse wastegate model may map a desired wastegate canister pressure or a desired wastegate valve position to a wastegate duty cycle for a given wastegate actuation force. Mapping to a wastegate duty cycle may include using look-up tables or calculating the wastegate duty cycle. The WGC signal may be pulse width modulated at the wastegate duty cycle to adjust the wastegate. The desired wastegate canister pressure or the desired wastegate valve position may be determined from feed-forward, feedback, or other control algorithms, for example.

The wastegate actuation force may also affect the dynamics of the wastegate. For example, canister volume236may fill faster at higher altitudes having lower atmospheric pressures than at lower altitudes having higher atmospheric pressures. A compensation term may account for delays of the wastegate actuator, as described herein with regard to the controller with zeros cancelling poles of the wastegate actuator model. The compensation term may be decreased for lower atmospheric pressures to account for faster dynamic actuation of the wastegate valve at lower atmospheric pressures. Similarly, the compensation term may be increased for higher atmospheric pressures to account for slower dynamic actuation of the wastegate valve at higher atmospheric pressures. Additionally, the compensation term may further include adjustments based on movement of twin independent cams, which can affect boost pressure. For example, as the intake cam is moved in a way that would increase boost pressure relative to atmospheric pressure, the magnitude of the compensation term may be decreased. Likewise, as the intake cam is moved in a way that would decrease boost pressure relative to atmospheric pressure, the magnitude of the compensation term may be increased.

In another example, the compensation term may be adjusted to account for blow-through (e.g. scavenging) operation with large valve overlap. In a turbocharged (boosted) engine, blow-through may occur when the intake pressure is higher than the exhaust pressure, and some amount of fresh air may flow directly from the intake manifold to the exhaust manifold during the valve overlap period without participating in cylinder combustion. Boosted engines may be intentionally operated in this way by advancing intake cam timing and retarding the exhaust cam timing to improve volumetric efficiency and reduce turbo lag. However, the blow-through air is cooler (because it is not combusted) and hence adds less energy to the exhaust system and the turbine compared to an engine without blow-through. To account for the blow-through air, the wastegate operation may be adjusted for the fraction of blow-through air by modifying the feedforward schedules and increasing the feedback gains. For example, increasing the compensation term may account for the lower exhaust energy that may result in lower gain in the feedback loop and slower system response without this adjustment. In yet another example, the compensation term may be adjusted to account for changes in boost pressure caused by movement of throttle plate164.

Next, at650, the wastegate may be adjusted according to the desired boost. For example, the desired boost may be used as an input to a feed-forward control algorithm for adjusting the wastegate. The feed-forward control algorithm may calculate a target wastegate canister pressure or a target wastegate valve position that may be used as a component of an input to the inverse wastegate model to determine the wastegate duty cycle.

Next, at660, a boost error may be calculated as a difference between the desired boost and the actual boost. The wastegate may be adjusted according to the boost error. For example, the boost error may be used as an input to a feedback control algorithm to calculate a target wastegate canister pressure or a target wastegate valve position that may be used as a component of an input to the inverse wastegate model to determine the wastegate duty cycle. The control algorithm may include a compensation term to account for delays caused by filling and emptying canister volume236. The magnitude of the compensation term may be increased as atmospheric pressure increases to account for slower filling and emptying of canister volume236. The magnitude of the compensation term may be decreased as atmospheric pressure decreases to account for faster filling and emptying of canister volume236.

In this manner, method600may be used to substantially reduce the interaction between powering wastegate177and controlling the boost. As further elaborated with reference toFIG. 7, a method700may be implemented using the steps of method600.

The desired boost pressure, actual boost pressure, and atmospheric pressure are determined and shown as inputs to method700. At710, wastegate actuation force715is a feedback component that is calculated from the difference between the actual boost pressure and atmospheric pressure. Wastegate actuation force715may be an input to inverse wastegate model720. A target wastegate canister pressure730may be used as another input to inverse wastegate model720. In an alternate embodiment, a target wastegate valve position may be used as another input to inverse wastegate model720. Inverse wastegate model720may map the target wastegate canister pressure730to wastegate duty cycle725for wastegate actuation force715. The WGC signal may be pulse width modulated at wastegate duty cycle725to adjust wastegate177of engine10. Plant740includes engine10.

Feed-forward control750includes the desired boost as an input to determine a feed-forward component755of the target wastegate canister pressure730. Feed-forward control750may include a static feed-forward term and/or a dynamic feed-forward term. The static feed-forward term may calculate a feed-forward component from one or more engine operating conditions, including the desired boost, for example. The dynamic feed-forward term may calculate a feed-forward component from a time rate of change of one or more engine operating conditions, including a time rate of change of the desired boost, for example. At760, boost error765may be calculated as a difference between the desired boost and the actual boost. Boost error765may be used as an input to feedback control770to determine a feedback component775of the target wastegate canister pressure730. Feedback control770may include a proportional-integral (PI) controller or a proportional-integral-derivative (PID) controller. Feedback control770may include a lead/lag filter, or compensation term, to account for the dynamics of wastegate canister230filling and emptying. The compensation term may be adjusted according to wastegate duty cycle725or wastegate actuation force715. For example, the feedback control770may have a transfer function such as:
−((twg*s+1)/(C1*s+1))*((kp*s+ki)/(s)),

where twg is the time constant of the wastegate, and C1may be experimentally determined for a system. In one embodiment, C1may be 0.05. The zero of the lead filter (1/twg) may be used to cancel the pole from the wastegate canister pressure dynamics. The zero of the PI controller (ki/kp) may be used to cancel the system pole (1/tsys), where tsys is the time constant of the open loop system.

The feed-forward component755and the feedback component775may be combined by adder780to obtain the target wastegate canister pressure730. In this manner, method700may substantially reduce the interaction between powering wastegate177and controlling the actual boost pressure.

Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.