Temperature management of catalyst system for a variable displacement engine

A system and method for controlling an internal combustion engine having a plurality of cylinders, at least some of which may be selectively deactivated to provide variable displacement operation, including temperature management of at least one engine/vehicle component by monitoring the temperature of the component and controlling activation of at least one cylinder to control the temperature of the component. In one embodiment, the engine/vehicle component is an emission control device, such as a catalytic converter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for controlling a variable displacement engine to manage temperature of a catalyst system.

2. Background Art

Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions. In some configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated.

Reducing the number of operating cylinders may also reduce the operating temperature of various engine and/or vehicle components, which may adversely affect desired engine operation. For example, certain emission control devices, such as catalytic converters, require a minimum operating temperature for efficient operation. One approach to raise catalyst temperature involves enriching the fuel supply to the operating cylinders when catalyst temperature drops below a specified level as disclosed in U.S. Pat. No. 4,467,602. This method assumes that excess air is available in the catalytic converter to be effective. The inventors herein have recognized that this assumption may not always be valid and may result in reduced catalyst and/or engine efficiency during certain operating conditions.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a system and method for controlling a variable displacement internal combustion engine to effectively manage the temperature of one or more engine and/or vehicle components.

In carrying out the above object and other objects, advantages, and features of the invention, a system and method for controlling a variable displacement internal combustion engine include controlling the number or ratio of active/inactive cylinders to control the temperature of at least one engine or vehicle component. In one preferred embodiment, the system and method include controlling a variable displacement engine having a bank configuration with a close-coupled catalyst associated with each bank of cylinders and at least one downstream or underbody catalyst by activating the second bank of cylinders when one of the catalysts is determined to be near or below a minimum efficient operating temperature.

The present invention provides a number of advantages. For example, the present invention manages the temperature of one or more engine/vehicle components to maintain a desired operating efficiency while also efficiently operating the engine.

The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A block diagram illustrating an engine control system for a representative internal combustion engine operable in a variable displacement mode to manage temperature of an engine/vehicle component according to the present invention is shown in FIG.1. System10preferably includes an internal combustion engine12having a plurality of cylinders, represented by cylinder14. In one preferred embodiment, engine12includes ten cylinders arranged in a “V” configuration having two cylinder banks with five cylinders each. As used herein, a cylinder bank refers to a related group of cylinders having a common characteristic, such as being located proximate one another, having a common emission control device (END), or related according to firing order, for example. As such, cylinder banks can also be defined for in-line cylinder configurations as well.

As one of ordinary skill in the art will appreciate, system10includes various sensors and actuators to effect control of the engine. One or more sensors or actuators may be provided for each cylinder14, or a single sensor or actuator may be provided for the engine. For example, each cylinder14may include four actuators which operate corresponding intake and exhaust valves, while only including a single engine coolant temperature sensor.

System10preferably includes a controller16having a microprocessor28in communication with various computer-readable storage media, indicated generally by reference numeral20. The computer readable storage media preferably include a read-only memory (ROM)22, a random-access memory (RAM)24, and a keep-alive memory (KAM)26. As known by those of ordinary skill in the art, KAM26is used to store various operating variables while controller16is powered down but is connected to the vehicle battery. Computer-readable storage media20may be implemented using any of a number of known memory devices such as PROMs, EPROMs, EEPROMs, flash memory, or any other electric, magnetic, optical, or combination memory device capable of storing data, some of which represents executable instructions, used by microprocessor28in controlling the engine. Microprocessor28communicates with the various sensors and actuators via an input/output (I/O) interface32. Of course, the present invention could utilize more than one physical controller, such as controller16, to provide engine/vehicle control depending upon the particular application.

In operation, air passes through intake34where it may be distributed to the plurality of cylinders via an intake manifold, indicated generally by reference numeral36. System10preferably includes a mass airflow sensor38which provides a corresponding signal (MAF) to controller16indicative of the mass airflow. If no mass airflow sensor is present, a mass airflow value may be inferred from various engine operating parameters. A throttle valve40may be used to modulate the airflow through intake34during certain operating modes. Throttle valve40is preferably electronically controlled by an appropriate actuator42based on a corresponding throttle position signal generated by controller16. A throttle position sensor provides a feedback signal (TP) indicative of the actual position of throttle valve40to controller16to implement closed loop control of throttle valve40.

As illustrated inFIG. 1, a manifold absolute pressure sensor46may be used to provide a signal (MAP) indicative of the manifold pressure to controller16. Air passing through intake34enters the combustion chambers or cylinders14through appropriate control of one or more intake valves. The intake and exhaust valves may be controlled directly or indirectly by controller16along with ignition timing (spark) and fuel to selectively activate/deactivate one or more cylinders12to provide variable displacement operation. A fuel injector48injects an appropriate quantity of fuel in one or more injection events for the current operating mode based on a signal (FPW) generated by controller16processed by an appropriate driver. Control of the fuel injection events is generally based on the position of the pistons within respective cylinders14. Position information is acquired by an appropriate crankshaft sensor which provides a position signal (PIP) indicative of crankshaft rotational position. At the appropriate time during the combustion cycle, controller16generates a spark signal (SA) which is processed by ignition system58to control spark plug60and initiate combustion within an associated cylinder14.

Controller16(or a camshaft arrangement) controls one or more exhaust valves to exhaust the combusted air/fuel mixture of activated or running cylinders through an associated exhaust manifold, indicated generally by reference numeral28. Depending upon the particular engine configuration, one or more exhaust manifolds may be used. In one preferred embodiment, engine12includes an exhaust manifold28associated with each bank of cylinders as illustrated in FIG.1.

An exhaust gas oxygen sensor62is preferably associated with each bank of cylinders and provides a signal (EGO) indicative of the oxygen content of the exhaust gases to controller16. The present invention is independent of the particular type of exhaust gas oxygen sensor utilized, which may depend on the particular application. In one embodiment, heated exhaust gas oxygen sensors (HEGO) are used. Of course, various other types of air/fuel ratio sensors/indicators may be used such as a universal exhaust gas oxygen sensor (UEGO), for example. The exhaust gas oxygen sensor signals may be used to independently adjust the air/fuel ratio, or control the operating mode of one or more cylinders or banks of cylinders. The exhaust gas passes through the exhaust manifolds28through associated upstream emission control devices64A and64B which may be catalytic converters, for example. After passing through the associated upstream ECDs, the exhaust gas is combined and flows past an underbody exhaust gas oxygen sensor66and through a downstream emission control device68before flowing past a catalyst monitoring sensor70(typically another exhaust gas oxygen sensor) and being exhausted to atmosphere.

A temperature sensor72may be provided to monitor the temperature of a catalyst within emission control device68, depending upon the particular application. Alternatively, the temperature may be estimated using an appropriate temperature model based on various other sensed engine/vehicle parameters which may include mass airflow, manifold absolute pressure or load, engine speed, air temperature, engine coolant temperature, and/or engine oil temperature, for example. A representative temperature model could be developed to determine catalyst temperature for any one of the emission control devices64A,64B and/or68using various sensed and estimated engine operating parameters as described in U.S. Pat. No. 5,956,941, for example.

According to the present invention, controller16manages temperature of one or more engine/vehicle components, such as emission control devices64A,64B, and/or68by controlling activation/deactivation of one or more cylinders. In a preferred embodiment, engine12is a V-10 engine with variable displacement operation provided by selectively deactivating one bank of cylinders under appropriate engine and/or vehicle operating conditions, such as light load, for example. The deactivated cylinder bank may then be selectively activated to maintain efficient operation of one or more emission control devices. For example, the second cylinder bank may be reactivated to maintain the temperature of emission control device68sufficiently above the catalyst light-off temperature to maintain efficient operation. The cylinder bank is then deactivated after the temperature exceeds a corresponding threshold to provide hysteresis, or to reduce the operating temperature to prolong component life, for example, as explained in greater detail below.

Referring now toFIG. 2, an alternative embodiment for controlling a variable displacement engine to manage temperature of an engine/vehicle component according to the present invention is shown. As will be recognized by those of ordinary skill in the art, system100includes similar components as described with reference to the embodiment illustrated in FIG.1and incorporated here by reference internal combustion engine102includes two cylinder banks104,106. Each cylinder bank includes an associated upstream or close-coupled emission control device108and110, respectively. In addition, rather than combining the exhaust and using a common third emission control device as illustrated inFIG. 1, each bank104,106also has an associated downstream or underbody emission control device112,114, respectively. In one embodiment, the emission control devices108,110,112, and114are three-way catalysts.

As also illustrated inFIG. 2, each END has an associated exhaust gas oxygen sensor116,118,120,122, respectively, which are preferably HEGO sensors. Additional exhaust gas oxygen sensors124,126may be provided downstream relative to downstream ECDs112,114, respectively, to provide a conversion efficiency indication and monitor operation of the emission control devices. Downstream ECDs112,114preferably include associated temperature sensors128.,130to provide an indication of the catalyst temperature which may be used by controller132to manage the temperature of one or more of the ECDs as described herein. It should be recognized by those of ordinary skill in the art that the temperature of one or more engine/vehicle components can be modeled as described above with reference to the embodiment illustrated in FIG.1. Component temperature modeling may be used alone or in combination with one or more temperature sensors to provide temperature management according to the present invention. One of ordinary skill in the art will also recognize that a variety of engine/vehicle operating parameters influence the current operating mode and selective activation/deactivation of one or more cylinders to provide variable displacement operation. These parameters may affect or override the decision to activate/deactivate cylinders to provide the temperature management features in accordance with the present invention.

The diagrams ofFIGS. 3 and 4generally represent control logic for one embodiment of a system or method according to the present invention. As will be appreciated by one of ordinary skill in the art, the diagrams may represent any one or more of a number of known processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages of the invention, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending upon the particular processing strategy being used.

Preferably, the control logic is implemented primarily in software executed by a microprocessor-based engine controller. Of course, the control logic may be implemented in software, hardware, or a combination of software and hardware depending upon the particular application. When implemented in software, the control logic is preferably provided in a computer-readable storage medium having stored data representing instructions executed by a computer to control the engine. The computer-readable storage medium or media may be any of a number of known physical devices which utilize electric, magnetic, and/or optical devices to temporarily or persistently store executable instructions and associated calibration information, operating variables, and the like.

Block150ofFIG. 3represents monitoring of at least one engine or vehicle component such as an emission control device (END). In this embodiment, block150determines whether an upstream END is above a corresponding or associated temperature threshold. For example, the temperature threshold may correspond to be light-off temperature of a three-way catalyst. Block152determines whether a downstream END is above a corresponding temperature. The downstream END may be associated with a single upstream device, as illustrated inFIG. 2, or shared by multiple upstream devices as illustrated in FIG.1. If the upstream END is above the corresponding temperature threshold as determined by block150and the downstream END is above its associated temperature threshold as determined by block152, all cylinders are operated under closed-loop control with a normal scheduled air/fuel ratio and spark or ignition timing as represented by block154.

If the upstream component is below its associated temperature threshold as indicated by block150, or the downstream component is below its associated temperature threshold as indicated by block152, block156determines whether an associated exhaust gas oxygen sensor is available in providing information sufficient to operate closed-loop. In this particular embodiment, block156determines whether an associated HEGO sensor has reached an appropriate operating temperature to provide reliable information with respect to the oxygen content of the exhaust gas. If the associated HEGO is ready for closed-loop operation as determined by block156, the previously deactivated cylinders are activated with a lean bias on the air/fuel ratio and spark retarded from MBT. The previously running or activated cylinders are operated with a rich bias air/fuel ratio. All cylinders are operated using closed-loop control of air/fuel ratio based on the HEGO sensor reading with appropriate lean/rich bias as represented by block158. In one embodiment, an entire bank of cylinders is activated and operated with a lean bias and retarded spark until the downstream END reaches its temperature threshold as determined by block152.

If the HEGO sensor associated with the END is not ready for closed-loop operation as determined by block156, the engine is controlled to activate the deactivated cylinders and operate them open-loop with a lean air/fuel ratio and spark retarded from MBT as represented by block160. The previously activated or running cylinders are operated with a rich bias air/fuel ratio in closed-loop mode.

FIG. 4provides an alternative representation of operation for a system or method to manage temperature of an engine/vehicle component according to the present invention. Block180represents monitoring of at least one catalyst temperature using a temperature model as represented by block182and/or an associated temperature sensor as represented by block184. The engine/vehicle component, in this embodiment a catalyst, is monitored and managed by controlling activation of at least one cylinder in a variable displacement operating mode to control the temperature of the component. In this example, block186compares the catalyst temperature to a low temperature threshold. If the temperature is below the associated low temperature threshold, block192activates one or more deactivated cylinders to raise the temperature of the catalyst. Block194controls the air/fuel ratio and/or spark using open-loop, closed-loop, or a combination, to control the various cylinders as described with reference toFIG. 3above. In one embodiment, block192activates an entire bank of deactivated cylinders. Preferably, control of the activated and deactivated cylinders is coordinated during reactivation such that the combined exhaust approaches a stoichiometric air/fuel ratio.

Block188ofFIG. 4represents comparing the catalyst temperature to an associated high temperature threshold to trigger deactivation of one or more cylinders as represented by block190. The comparison represented by block188may be used to provide appropriate hysteresis to avoid hunting or recycling of the deactivated cylinders. Alternatively, or in combination, a temperature threshold may be provided as one form of component protection to reduce or represent premature reduction of the catalyst conversion efficiency.

As such, the present invention manages the temperature of one or more engine/vehicle components such as an emission control device to maintain a desired operating efficiency while also efficiently operating the engine.