Abstract:
A system includes a fuel cutoff module and a cylinder deactivation module. The fuel cutoff module generates a fuel cutoff signal when a deceleration fuel cutoff condition occurs, wherein fueling to M cylinders of an engine is disabled based on the fuel cutoff signal, and wherein M is an integer greater than or equal to one. The cylinder deactivation module deactivates the M cylinders in response to the fuel cutoff signal.

Description:
FIELD 
       [0001]    The present disclosure relates to engine control systems, and more particularly to systems and methods for reducing fuel enrichment after fuel cutoff modes. 
       BACKGROUND 
       [0002]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0003]    Engines emit exhaust gas that includes carbon dioxide, water, carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), and other compounds. Exhaust systems typically include a catalyst that reduces the levels of CO, NOx, and HC in the exhaust gas by chemically converting these gases into carbon dioxide, nitrogen, and water. The catalyst reduces the levels of the gases by catalyzing a reaction between the gases and oxygen. The catalyst stores oxygen when operating under lean fuel conditions and releases oxygen when operating under rich fuel conditions. 
         [0004]    A vehicle may operate in a fuel cutoff mode during which fueling to the cylinders is disabled. The fuel cutoff mode may occur when the vehicle is decelerating with no throttle input from a driver and the engine is acting as a brake. During the fuel cutoff mode, the engine pumps air through the exhaust system rather than exhaust gas, resulting in delivery of excess oxygen to the catalyst. The catalyst stores the oxygen until a maximum oxygen storage amount is reached. When the maximum oxygen storage amount is exceeded, the ability of the catalyst to convert NOx emissions may be substantially reduced, resulting in NOx breakthrough. Therefore, when fueling resumes, an increased amount of fueling is delivered to the engine to cause rich fuel conditions. The rich fuel conditions decrease the amount of oxygen and improves NOx conversion. 
       SUMMARY 
       [0005]    A system includes a fuel cutoff module and a cylinder deactivation module. The fuel cutoff module generates a fuel cutoff signal when a deceleration fuel cutoff condition occurs, wherein fueling to M cylinders of an engine is disabled based on the fuel cutoff signal, and wherein M is an integer greater than or equal to one. The cylinder deactivation module deactivates the M cylinders in response to the fuel cutoff signal. 
         [0006]    A method includes generating a fuel cutoff signal when a deceleration fuel cutoff condition occurs, wherein fueling to M cylinders of an engine is disabled based on the fuel cutoff signal, and wherein M is an integer greater than or equal to one, and deactivating the M cylinders in response to the fuel cutoff signal. 
         [0007]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a functional block diagram of an exemplary engine system according to the principles of the present disclosure; 
           [0009]      FIG. 2  is a functional block diagram of an engine control module according to the principles of the present disclosure; and 
           [0010]      FIG. 3  is a flowchart that illustrates a method performed by the engine control module according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 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 steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0012]    As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0013]    During the fuel cutoff mode, excess oxygen is stored by the catalyst, increasing the oxygen storage amount of the catalyst and reducing the ability of the catalyst to convert NOx emissions. When fueling resumes, increased fueling reduces the oxygen storage amount. However, the increased fueling reduces fuel efficiency and may require additional time to reduce the oxygen storage amount. Thus, it is desirable to prevent increases in the oxygen storage amount when the vehicle operates in the fuel cutoff mode. Preventing an increase in the oxygen storage amount reduces the need for fuel enrichment when the fuel cutoff mode ends. 
         [0014]    An enrichment reduction system according to the present disclosure decreases the amount of air pumped through the catalyst during the fuel cutoff mode. The enrichment reduction system determines when fuel to a cylinder has been disabled in fuel cutoff mode. The enrichment reduction system deactivates the cylinder to prevent air from being pumped by the cylinder through the exhaust system during the fuel cutoff mode. When fueling resumes, the need for fuel enrichment of the engine is reduced. 
         [0015]    Referring now to  FIG. 1 , a functional block diagram of an exemplary engine system  100  is presented. The engine system  100  includes an engine  102  that combusts an air/fuel mixture to produce drive torque for a vehicle based on output from a driver input module  104 . For example only, the driver input module  104  may output a position signal based on a position of an accelerator input device, such as an accelerator pedal. 
         [0016]    The engine  102  draws air into an intake manifold  110  through a throttle valve  112 . For example only, the throttle valve  112  may include a butterfly valve having a rotatable blade. An engine control module (ECM)  114  controls a throttle actuator module  116 , which regulates opening of the throttle valve  112  to control the amount of air drawn into the intake manifold  110 . The ECM  114  may implement the enrichment reduction system of the present disclosure. Air from the intake manifold  110  flows into cylinders of the engine  102 . While the engine  102  may include multiple cylinders, for illustration purposes a single representative cylinder  118  is shown. For example only, the engine  102  may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. 
         [0017]    An intake valve  122  regulates the flow of air from the intake manifold  110  into the cylinder  118 . The ECM  114  controls a fuel actuator module  124 , which regulates fuel injection to achieve a desired air/fuel ratio. Fuel may be injected into the intake manifold  110  at a central location or at multiple locations, such as near the intake valve of each of the cylinders. In various implementations not depicted in  FIG. 1 , fuel may be injected directly into the cylinders or into mixing chambers associated with the cylinders. The fuel actuator module  124  may halt injection of fuel to cylinders during a fuel cutoff mode. 
         [0018]    The injected fuel mixes with air and creates an air/fuel mixture in the cylinder  118 . A piston (not shown) within the cylinder  118  compresses the air/fuel mixture. Based upon a signal from the ECM  114 , a spark actuator module  126  may energize a spark plug  128  in the cylinder  118 , 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). In diesel engines, the spark actuator module  126  and spark plug  128  may be omitted. 
         [0019]    The combustion of the air/fuel mixture drives the piston down, thereby driving a rotating crankshaft (not shown). The piston then begins moving up again and expels the byproducts of combustion through an exhaust valve  130 . The byproducts of combustion including exhaust gas are exhausted from the vehicle via an exhaust system  132 . 
         [0020]    A catalyst  134  in the exhaust system  132  reduces amounts of gases such as CO, HC, and NOx emitted by the engine  102 . The catalyst  134  reduces the amounts of the gases by catalyzing a reaction between the gases and oxygen. The catalyst  134  includes a property known as oxygen storage capacity (OSC). OSC refers to an ability of the catalyst  134  to store excess oxygen when the engine  102  operates under lean conditions and to release oxygen when the engine  102  operates under rich conditions. The amount of oxygen stored by the catalyst may be referred to as an oxygen storage amount. Lean conditions may occur when the ratio of the air/fuel mixture is greater than a stoichiometric air/fuel mixture. Rich conditions may occur when the ratio of the air/fuel mixture is less than a stoichiometric air/fuel mixture. 
         [0021]    The oxygen storage amount may increase or decrease depending on the ratio of the air/fuel mixture. During lean conditions, the oxygen storage amount may increase because the air/fuel mixture includes excess oxygen. During rich conditions, the stored oxygen may decrease because the air/fuel mixture includes excess fuel. The excess oxygen is stored in the catalyst  134  until a maximum storage amount is attained. The maximum storage amount may depend on the size and composition of the catalyst  134 . The maximum storage amount may depend on the temperature of the catalyst  134 . When the catalyst  134  reaches the maximum storage amount, NOx breakthrough may occur, reducing the ability of the catalyst  134  to convert NOx emissions. 
         [0022]    A vehicle may operate in a fuel cutoff mode in which the fuel actuator module  124  cuts off fueling (i.e., stops fuel flow) to one or more cylinders. Fuel cutoff mode may occur when the vehicle is operating in an “overrun” or “deceleration” condition. A vehicle traveling with no throttle input from the driver (i.e., no input to the accelerator input device) and the engine  102  acting as a brake (i.e., producing negative torque) may be described as operating in the overrun or deceleration condition. When deceleration conditions exist, fueling may be disabled in a deceleration fuel cutoff (DFCO) mode. DFCO mode may be implemented to increase fuel economy and/or increase engine braking. During DFCO mode, the engine  102  pumps air through the exhaust system  132 , resulting in delivery of excess oxygen to the catalyst  134 . 
         [0023]    Oxygen sensors may be used to determine amounts of oxygen in the exhaust gas. The oxygen sensors generate oxygen signals that indicate oxygen amounts in the exhaust gas. A first oxygen sensor  136  may generate an upstream oxygen signal that indicates an oxygen amount upstream from the catalyst  134 . A second oxygen sensor  138  may generate a downstream oxygen signal that indicates an oxygen amount downstream from the catalyst  134 . The ECM  114  may determine the oxygen storage amount based on the upstream and/or the downstream oxygen signals. 
         [0024]    An intake camshaft  140  may control opening and closing of the intake valve  122 . An exhaust camshaft  142  may control opening and closing of the exhaust valve  130 . In various implementations, multiple intake camshafts may control multiple intake valves per cylinder and/or may control the intake valves of multiple banks of cylinders. Similarly, multiple exhaust camshafts may control multiple exhaust valves per cylinder and/or may control exhaust valves for multiple banks of cylinders. A single camshaft may control opening and closing of the intake valve  122  and the exhaust valve  130 . 
         [0025]    A cylinder actuator module  144  may deactivate the cylinder  118  by disabling opening of the intake valve  122  and/or the exhaust valve  130 . In various implementations, the cylinder actuator module  144  may include a hydraulic system that selectively decouples the intake and/or exhaust valves from the corresponding camshafts for one or more cylinders in order to deactivate those cylinders. For example only, valves for half of the cylinders are either hydraulically coupled or decoupled as a group by the cylinder actuator module  144 . 
         [0026]    A temperature sensor  170  may indicate the temperature (T C ) of the catalyst  134 . A vehicle speed sensor  172  may indicate the speed of the vehicle (VS) based on a rotational velocity of a drive wheel or an output speed of a transmission. An RPM sensor  180  may measure the speed of the crankshaft in revolutions per minute (RPM). An engine coolant temperature (ECT) sensor  182  may indicate a temperature of coolant in the engine  102  and/or the engine  102 . The ECT sensor  182  may be located within the engine  102  or at other locations where the coolant is circulated, such as a radiator (not shown). 
         [0027]    A manifold absolute pressure (MAP) sensor  184  may indicate pressure within the intake manifold  110 . In various implementations, the MAP sensor  184  may measure engine vacuum, which is the difference between ambient air pressure and the pressure within the intake manifold  110 . A mass airflow (MAF) sensor  186  measures a mass flow rate of air flowing into the intake manifold  110 . In various implementations, the MAF sensor  186  may be located in a housing that also includes the throttle valve  112 . 
         [0028]    The throttle actuator module  116  may monitor the position of the throttle valve  112  using one or more throttle position sensors (TPS)  190 . An intake air temperature (IAT) sensor  192  may measure the ambient temperature of air being drawn into the engine  102 . Other sensors  194  may include other temperature sensors in the exhaust system  132 , camshaft position sensors, and other engine sensors. The ECM  114  may use signals from the sensors to make control decisions for the engine system  100 . 
         [0029]    Each system that varies an engine parameter may be referred to as an actuator that receives an actuator value. For example, the throttle actuator module  116  may be referred to as an actuator and the throttle opening area may be referred to as the actuator value. In the example of  FIG. 1 , the throttle actuator module  116  achieves the throttle opening area by adjusting the angle of the blade of the throttle valve  112 . 
         [0030]    Similarly, the spark actuator module  126  may be referred to as an actuator, while the corresponding actuator value may be the amount of spark advance relative to cylinder TDC. Other actuators may include the fuel actuator module  124  and the cylinder actuator module  144 . For these actuators, the actuator values may correspond to fueling rate and number of cylinders and/or valves activated, respectively. The ECM  114  may control actuator values in order to generate a desired torque from the engine  102 . The ECM  114  may control actuator values to implement the enrichment reduction system of the present disclosure. 
         [0031]    Referring now to  FIG. 2 , a functional block diagram of an exemplary engine control module (ECM)  114  includes a deceleration fuel cutoff (DFCO) module  202 , an oxygen storage module  204 , and a cylinder deactivation module  206 . The DFCO module  202  may generate a fuel cutoff signal when overrun conditions exist. Fueling to the cylinder  118  is disabled in response to the fuel cutoff signal. The oxygen storage module  204  determines the oxygen storage amount of the catalyst  134 . The cylinder deactivation module  206  deactivates the cylinder  118  in response to the fuel cutoff signal and the oxygen storage amount. 
         [0032]    The DFCO module  202  may enter DFCO mode when overrun conditions occur. Overrun conditions may occur based on input from the driver input module  104 , the vehicle speed sensor  172 , and the temperature sensor  170 . For example only, when vehicle speed is greater than a speed threshold, the temperature of the catalyst  134  is less than a temperature threshold, and the position of the accelerator input device is less than a position threshold, the DFCO module  202  may enter DFCO mode. The DFCO module  202  may generate a fuel cutoff signal when in DFCO mode. The fuel actuator module  124  may halt injection of fuel to the cylinder  118  based on the fuel cutoff signal. The fuel actuator module  124  may halt injection of fuel to all cylinders of the engine  102  based on the fuel cutoff signal. 
         [0033]    The oxygen storage module  204  determines the oxygen storage amount of the catalyst  134 . The oxygen storage module  204  may determine the oxygen storage amount while the engine  102  is being fueled and during the DFCO mode. For example only, the oxygen storage module  204  may determine the oxygen storage amount at a time before the DFCO module  202  cuts fuel. 
         [0034]    The oxygen storage amount may be determined based on oxygen amounts indicated by one or more of the oxygen sensors  136  and  138 . For example only, when the second oxygen sensor  138  indicates an oxygen amount that is greater than a threshold oxygen amount, the oxygen storage module  204  may determine the oxygen storage amount is greater than a threshold storage amount. The threshold storage amount may be an amount of oxygen that indicates NOx breakthrough. 
         [0035]    The cylinder deactivation module  206  receives the fuel cutoff signal and the oxygen storage amount and determines whether to deactivate cylinders. The cylinder deactivation module  206  may deactivate the cylinder  118  in response to the fuel cutoff signal. The cylinder deactivation module  206  may monitor the oxygen storage amount during the DFCO mode and deactivate the cylinder  118  when the oxygen storage amount is greater than the threshold storage amount. The cylinder deactivation module  206  may deactivate one or more valves to deactivate the cylinder  118 . The exhaust valve  130  may be deactivated to prevent exhaust gas from exiting the cylinder  118 . The intake valve  122  may be deactivated to prevent fresh air from entering the cylinder  118 . 
         [0036]    The cylinder deactivation module  206  may deactivate the valves in various sequences and at various times. For example only, the valves may be deactivated such that a charge of exhaust gas is trapped within the cylinder  118 . The intake valve  122  may be deactivated after an intake stroke of the piston. The exhaust valve  130  may be deactivated prior to the subsequent exhaust stroke of the piston. 
         [0037]    The cylinder deactivation module  206  may instruct the cylinder actuator module  144  to deactivate one or more cylinders of the engine  102 . In various implementations, a predefined group of cylinders may be deactivated jointly. The cylinder deactivation module  206  may also instruct the spark actuator module  126  to stop providing spark for deactivated cylinders. 
         [0038]    By deactivating cylinders during DFCO mode, the engine  102  pumps less air through the exhaust system  132  than when the cylinders are active but not fueled. Decreasing the amount of air flowing through the exhaust system  132  reduces the amount of oxygen entering the catalyst  134 . Thus, the oxygen storage amount of the catalyst  134  may not increase during DFCO mode. When DFCO mode ends and fueling resumes, less fuel is required to reduce the oxygen storage amount, resulting in improved fuel efficiency of the engine system  100 . 
         [0039]    Referring now to  FIG. 3 , a flowchart  300  illustrates exemplary steps performed by the ECM  114 . Control begins in step  302  when control determines whether deceleration fuel cutoff (DFCO) mode has been entered. Control may enter DFCO mode when overrun conditions exist, and the DFCO module  202  may generate the fuel cutoff signal. When DFCO mode is entered, control proceeds to step  304 . 
         [0040]    In step  304 , control may determine the oxygen storage amount of the catalyst  134 . For example only, control may determine the oxygen storage amount based on the oxygen signals from the oxygen sensors  136  and  138 . In step  306 , control compares the oxygen storage amount to the threshold storage amount. When the oxygen storage amount is greater than the threshold storage amount, control may proceed to step  308 . Otherwise, control may continue to monitor the stored oxygen amount in step  304 . In step  308 , control deactivates one or more valves of one or more cylinders to prevent airflow to the catalyst  134  during DFCO mode. 
         [0041]    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 to the skilled practitioner upon a study of the drawings, the specification, and the following claims.