Abstract:
A method for controlling exhaust emissions is disclosed. The method includes producing exhaust having hydrocarbons and directing the exhaust through a converter. The method also includes directing the exhaust from the converter to an environment and determining a first rate indicative of a rate of hydrocarbons directed to the environment. The method further includes comparing the first rate with a predetermined rate and adjusting the production of exhaust, if the first rate is greater than the predetermined rate.

Description:
TECHNICAL FIELD  
       [0001]     This disclosure relates to a system for controlling emissions, and more particularly to a method and apparatus for controlling exhaust emissions.  
       BACKGROUND  
       [0002]     Combustion engines, such as, for example, compression or spark ignition engines, can produce a variety of byproducts that may be environmentally harmful, such as, for example, nitric oxides, sulfur-containing acidic species, and/or hydrocarbons. Various systems and methods have been used to minimize the release of such byproducts to the environment. For example, new fuels are being developed which lower the levels of sulfur-acids produced during fuel combustion. Additionally, exhaust systems are available which absorb, e.g., by trapping, and/or convert, e.g., by transforming into innocuous substances, harmful chemicals before release to the environment.  
         [0003]     Usually, engine exhaust systems include one or more catalysts that are configured to absorb and/or convert hydrocarbons and thus reduce potentially harmful exhaust emissions to the environment. Often, such catalysts have an optimum temperature range for absorption of hydrocarbons. Specifically, such catalysts, may be incapable or less capable of absorbing and/or converting hydrocarbons when cold, e.g., after a cold engine start or after extended periods of engine idling, as when warm. Until cold catalysts are heated above a threshold temperature, significant amounts of hydrocarbons may be released to the environment.  
         [0004]     U.S. Pat. No. 6,666,021 (“the &#39;021 patent”) issued to Lewis et al. discloses a method for adaptive engine control for vehicle starting. The system of the &#39;021 patent compares an exhaust temperature, subsequent to engine cranking, to a predetermined temperature. If the exhaust temperature is below the predetermined temperature, the engine is operated in a cold mode to minimize emissions of hydrocarbons to a cold catalyst. A cold mode operation provides a lean air-fuel ratio and retards the ignition timing to minimize hydrocarbon emissions. The system of the &#39;021 patent, monitors the exhaust temperature and subsequently operates the engine in a run mode when the exhaust temperature is above the predetermined temperature.  
         [0005]     Although the system of the &#39;021 patent may minimize hydrocarbon emissions during a cold mode, the system of the &#39;021 patent estimates the operability of the catalyst based on exhaust temperatures. Additionally, the system of the &#39;021 patent may inadequately estimate when the catalyst is within a suitable temperature range and may unnecessarily sacrifice engine performance for lower emissions when the catalyst may be capable of absorbing and/or converting a sufficient amount of hydrocarbons from the exhaust.  
         [0006]     The present disclosure is directed at overcoming one or more of the shortcomings set forth above.  
       SUMMARY OF THE INVENTION  
       [0007]     In a first aspect, the present disclosure is directed to a method for controlling exhaust emissions. The method includes producing exhaust having hydrocarbons and directing the exhaust through a converter. The method also includes directing the exhaust from the converter to an environment and determining a first rate indicative of a rate of hydrocarbons directed to the environment. The method further includes comparing the first rate with a predetermined rate and adjusting the production of exhaust, if the first rate is greater than the predetermined rate.  
         [0008]     In another aspect, the present disclosure is directed to a system for monitoring emissions. The system includes an engine configured to produce hydrocarbons at a first rate. The system also includes a converter configured to convert hydrocarbons at a second rate and release hydrocarbons to an environment at a third rate. The system further includes a controller configured to adjust parameters of the engine to produce hydrocarbons at a fourth rate less than the first rate when the third rate is greater than a predetermined rate.  
         [0009]     In yet another aspect, the present disclosure is directed to a method of operating an engine. The method includes monitoring at least one engine parameter indicative of an operational condition of an engine configured to produce exhaust including hydrocarbons. The method also includes monitoring a temperature and a pressure, each indicative of an operational condition of a converter, the converter including a catalyst configured to convert the hydrocarbons at a first rate and release the hydrocarbons to an environment at a second rate. The method further includes changing a status of the engine when the second rate is greater than a predetermined rate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic illustration of an engine exhaust system in accordance with the present disclosure; and  
         [0011]      FIG. 2  is a schematic illustration of an exemplary control logic executable by the controller of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0012]      FIG. 1  illustrates an exemplary exhaust system  10 . Exhaust system  10  may include an engine  12 , a converter  14 , and a controller  18  configured to control engine  12 . Exhaust system  10  may be configured to direct an exhaust produced by engine  12  through converter  14  to an environment  16 . Specifically, engine  12  may produce an exhaust as a byproduct of a combustion process and exhaust system  10  may be configured to direct the exhaust through converter  14  and toward environment  16 . It is contemplated that exhaust system  10  may include additional components such as, for example, a manifold, a recirculation device, a muffler, and/or other components known in the art. It is also contemplated that environment  16  may include any type of environment known in the art, such as, for example, an atmosphere.  
         [0013]     Engine  12  may include, for example, a diesel engine, a gasoline engine, a gaseous fuel driven engine, or any other engine known in the art. Engine  12  may be configured to supply power to operatively connected loads, such as, for example, traction devices, hydraulic pumps, and/or other loads known in the art. Specifically, engine  12  may be configured to operate in one or more operational modes in which engine  12  may have different operating conditions. For example, engine  12  may be configured to operate in a first mode in which an exhaust is produced including an amount of hydrocarbons less than an amount of hydrocarbons produced in a second mode. Engine  12  may be controlled to operate in different modes by controller  18  as a function of a determined desired status of engine  12 . It is contemplated that engine  12  may include one or more piston-cylinder arrangements disposed in an “in-line” or “V” configuration defining combustion chambers and connected to a crankshaft, one or more valves operatively associated with the combustion chambers to affect the flow of fluids into and out of the combustion chambers, and a fuel delivery system configured to deliver fuel to the combustion chamber as is conventional in the art. It is also contemplated that engine  12  may capable of operating in any number of different modes in which operational parameters, such as, for example, fuel delivery timing, valve timing, ignition timing, clean exhaust recirculation amounts, fuel amounts, and/or any other parameter known in the art may be varied either in conjunction or independently. It is further contemplated that engine  12  may, alternatively, include a rotary engine.  
         [0014]     Converter  14  may include any conventional catalyst device such as, for example, a catalyst trap, a catalytic converter, and/or a particulate filter, and may be configured to absorb and/or convert hydrocarbons. Specifically, converter  14  may include a catalyst such as, for example, platinum or ammonia, in any mass phase, such as, for example, gaseous, aqueous, or solid, configured to absorb and/or convert hydrocarbons present within an exhaust. Converter  14 , via the catalyst, may convert hydrocarbons into innocuous elements or molecules such as, for example, inert gases and/or water. Converter  14 , via the catalyst, may absorb hydrocarbons by physically trapping molecules within the catalyst and/or any other suitable filter. It is contemplated that converter  14 , and in particular, the catalyst, may be less active, e.g., may be less capable of absorbing and/or converting hydrocarbons, within certain temperature ranges. For example, the catalyst may, above a first threshold temperature, be capable of absorbing and/or converting substantially all hydrocarbons from an exhaust, may below the first threshold temperature and above a second threshold temperature be capable of absorbing and/or converting significantly less hydrocarbons from an exhaust, and may below the second threshold temperature be capable of absorbing and/or converting substantially no hydrocarbons from an exhaust. It is also contemplated that first and second threshold temperatures may be any temperature and may be dependent upon the type of catalyst. It is further contemplated that an innocuous substance may be any substance less harmful to environment  16  than the hydrocarbons produced by engine  12 .  
         [0015]     Controller  18  may be configured to affect the operation of engine  12  between the different modes. Controller  18  may include one or more microprocessors, a memory, a data storage device, a communications hub, and/or other components known in the art. It is contemplated that controller  18  may be integrated within a general control system capable of controlling additional various functions of a exhaust system  10  and/or system other than exhaust system  10 . Controller  18  may be configured to receive input signals from sensors  20 ,  22 ,  24 ,  26  via respective communication lines. Controller  18  may perform one or more algorithms to determine appropriate output signals to affect the operation of engine  12  and may deliver the output signals via one or more suitable communication lines. It is contemplated that controller  18  may be further configured to receive additional inputs indicative of various operating parameters of exhaust system  10 , such as, for example, exhaust flow rate.  
         [0016]     Sensors  20 ,  22  may include any conventional sensor configured to deliver a signal indicative of a temperature. Sensor  20  may be disposed between engine  12  and converter  14  and may be configured to communicate a signal indicative of a temperature of an exhaust upstream of converter  14 . Sensor  22  may be disposed between converter  14  and environment  16  and may be configured to communicate a signal indicative of a temperature of an exhaust downstream of converter  14 . Sensor  24  may include any conventional sensor configured to deliver a signal indicative of a pressure. Sensor  24  may be disposed relative to converter  14  and may be configured to communicate a signal indicative of a pressure within converter  14 , e.g., indicative of the pressure of an exhaust within converter  14 . It is contemplated that sensors  20 ,  22 ,  24  may be disposed at any location suitable for sensing and communicating temperature or pressure, as desired. It is also contemplated that sensors  20 ,  22 ,  24  may be configured to communicate any type of signal such as, for example, a voltage or a current.  
         [0017]     Sensor  26  may include any conventional sensor configured to deliver a signal indicative of an operating parameter of engine  12 . For example, sensor  26  may include one or more sensors disposed relative to components of engine  12  and may be configured to communicate signals indicative of one or more parameters, such as, for example, rotational speed of a crankshaft, valve position, air-fuel ratio, temperature, pressure, and/or any other parameter known in the art.  
         [0018]      FIG. 2  illustrates an exemplary status logic  30  which controller  18  may perform to determine a desired status of engine  12 . Status logic  30  may receive inputs from sensors  20 ,  22 ,  24 ,  26  and determine a status output  60  with which controller  18  may affect the operation of engine  12 , e.g., controller  18  may control engine  12  to operate in a desired mode as a function of engine status  60 . Specifically, status logic  30  may receive a first temperature input  32  from sensor  22  indicative of a temperature of exhaust upstream of converter  14  and may receive a second temperature input  34  from sensor  24  indicative of a temperature of exhaust downstream of converter  14 . Status logic  30  may receive a pressure input  36  from sensor  26  indicative of a pressure within converter  14  and may receive an engine input  40  indicative of an operational parameter of engine  12 . It is contemplated that engine input  40  may include one or more inputs indicative of one or more operating parameters of engine  12 , such as, for example, rotational speed of a crankshaft, fuel consumption, and/or torque output. It is also contemplated that status logic  30  may receive inputs from additional sensors indicative of additional operational parameters of exhaust system  10 , such as, for example, exhaust flow rate.  
         [0019]     Status logic  30  may include one or more algorithms configured to be performed and/or executed by controller  18  to determine a desired operating status of engine  12 . Specifically, status logic  30  may include one or more databases, two- or three-dimensional maps, look-up tables, equations, functions, and/or any other mathematical relationship known in the art. Status logic  30  may manipulate inputs received from sensors  20 ,  22 ,  24 ,  26  as a function of one or more variable or non-variable parameters, and/or predetermined constants, to determine status output  60 . For example, status logic  30  may be configured to determine if a rate of hydrocarbons released to environment  16  by converter  14 , e.g., that converter  14  has not absorbed and/or converted from the exhaust, is above a predetermined value. Controller  18  may be configured to vary one or more parameters of engine  12  as a function of status output  60 , to reduce the amount of hydrocarbons produced by engine  12 . It is noted that the references within the description of status logic  30  set forth below regarding algorithms including a particular mathematical relationship, e.g., an equation or a two-dimensional map, are for exemplary purposes only and it is contemplated that controller  18  may perform algorithms via any suitable mathematical relationship known in the art, e.g., an equation, any-dimensional map, a physics based model, an empirical model, and/or a look-up table, to determine a desired variable. It is contemplated that each and/or any of the variables determined via one or more algorithms within status logic  30  may include predetermined minimum and/or maximum values which status logic  30  may utilize within subsequent algorithms regardless of the determined variable as is conventional in the art. For example, one or more of the mathematical relationships within status logic  30  may determine a first variable by a division of a second variable that could be zero. As such, status logic  30  may determine the first variable to be a predetermined maximum value instead of determining the first variable to be a mathematical unknown, e.g., a positive number divided by zero.  
         [0020]     Step  42  may be configured to determine a rate of hydrocarbons produced (d_Produced/d_Time) by engine  12 . Specifically, step  42  may include one or more two- or three-dimensional maps and may be configured to determine an amount of hydrocarbons produced by engine  12  per a unit time. For example, step  42  may include one or more maps configured to relate engine input  40  and predetermined rates of hydrocarbon produced.  
         [0021]     Step  44  may be configured to determine a temperature indicative of an average temperature (Avg-Temp) of converter  14 . Specifically step  44  may include one or more equations configured to functionally relate temperature inputs  32 ,  34  to determine an average thereof as is conventional in the art. Hereinafter the temperature as determined in step  44  will be referenced as an average converter temperature, however, it is noted that the temperature determined in step  44  may be indicative of the average temperature of converter  14  and may or may not be equal to an actual average temperature of converter  14 .  
         [0022]     Step  46  may be configured to determine a rate of hydrocarbons converted (d_Converted/d_Time), e.g., converted into an innocuous substance, by converter  14  and may include one or more equations and/or one or more two- or three-dimensional maps. Specifically, step  46  may compare a current average converter temperature, e.g., the average converter temperature determined in step  44 , a previous average converter temperature, e.g., an average converter temperature determined when controller  18  performed a prior sequence of status logic  30 , and an elapsed time since determining the previous average temperature to determine a rate of change in average temperature of converter  14  (d_Avg-Temp/d_Time). It is contemplated that a previous average converter temperature, e.g., zero, may be assumed when controller  18  performs the first sequence of status logic  30 .  
         [0023]     Additionally, step  46  may determine a current available hydrocarbon conversion capacity of converter  14  via one or more two- or three-dimensional maps relating average converter temperatures and predetermined hydrocarbon conversion capacities of converter  14 . For example, step  46  may determine a capacity as a function of the current average converter temperature via one or more two- or three-dimensional maps relating capacity and temperatures. Step  46  may further compare the current capacity of converter  14 , a previously determined capacity of converter  14 , e.g., a determined capacity determined when controller  18  performed a prior sequence of status logic  30 , and a change between the current and previous average temperatures to determine a change in hydrocarbon conversion capacity relative to a change in temperature (d_Converted/d_Avg-Temp). It is contemplated that the conversion capacity of converter  14  may be indicative of the rate of hydrocarbons converted by converter  14 . For example, converter  14  may be configured to convert hydrocarbons at substantially full capacity less an efficiency factor. As such, step  46  may relate the determined rate of change of average temperatures (d_Avg-Temp/d_Time) and the determined change in hydrocarbon conversion capacity relative to the change in temperature (d_Converted/d_Avg-Temp) to determine a hydrocarbon conversion rate (d_Converted/d_Time). It is also contemplated that a previously determined capacity of converter  14 , e.g., 100%, may be assumed when controller  18  performs the first sequence of status logic  30 .  
         [0024]     Step  48  may be configured to determine a rate of hydrocarbons released (d_Released/d_Time), e.g., a rate of hydrocarbons that are neither absorbed nor converted by converter  14 . Specifically, step  48  may include one or more two- or three-dimensional maps configured to relate the current average converter temperature, a cumulative amount of hydrocarbons absorbed by converter  14 , and predetermined amounts of hydrocarbons released by converter  14 . It is contemplated that the cumulative amount of hydrocarbons absorbed by converter  14  may be determined in step  56 , however, an initial amount of hydrocarbons absorbed by converter  14 , e.g., zero, may be assumed when controller  18  performs the first sequence of status logic  30 .  
         [0025]     Step  50  may be configured to determine a standardizing factor and may include one or more equations and/or one or more two- or three-dimensional maps. Specifically, step  50  may be configured to determine a standardizing factor as a function of a space velocity of converter  14 . For example, the average converter temperature may be functionally related with an appropriate universal gas constant and pressure input  36  to establish a density of the exhaust. Step  50  may additionally include receiving additional parameters to determine a mass flow rate of exhaust which may be functionally related with the density to determine a gas flow rate which may be functionally related with a volume of converter  14  to establish a space velocity (Gas_flowrate/Volume). Step  50  may further include one or more two- or three-dimensional maps relating space velocities and predetermined standardized factors. As such, a determined standardized factor may be configured to adjust a determined rate of hydrocarbons released, as determined in step  48 , as a function of operational conditions of exhaust system  10 . It is contemplated that step  50  may resolve received inputs according to any system of units known in the art. It is also contemplated that an exhaust rate may be established in any suitable manner known in the art, such as, for example, as a function of one or more operating parameters of engine  12  or flow meters disposed within exhaust system  10 .  
         [0026]     Step  52  may be configured to determine a standardized rate of hydrocarbons released by converter  14  (d_Released′/d_Time). Specifically, step  52  may include one or more equations configured to functionally relate the determined rate of hydrocarbons released by converter  14 , as determined in step  48 , and the determined standardized factor, as determined in step  50 , to approximate the determined rate of hydrocarbons released as a function of the current operating conditions of exhaust system  10 , e.g., average temperature, pressure, or flow rate, of exhaust system  10 . As such, step  52  may adjust the rate of hydrocarbons released as a function of current operating conditions to, for example, improve the accuracy of the determined rate of hydrocarbons.  
         [0027]     Step  54  may be configured to determine a rate of hydrocarbons absorbed by converter  14 . Specifically, step  54  may resolve the rate of hydrocarbons produced by engine  12  (d_Produced/d_Time), the rate of hydrocarbons converted by converter  14  (d_Converted/d_Time) and the standardized rate of hydrocarbons released by converter  14  (d_Released′/d_Time). For example, step  54  may functionally combine the rate of hydrocarbons produced by engine  12 , the rate of hydrocarbons converted by converter  14 , and the rate of hydrocarbons released by converter  14  to determine the rate of hydrocarbons absorbed by converter  14  (d_Absorbed/d_Time). It is contemplated that step  54  may functionally subtract the rate of hydrocarbons converted and the rate of hydrocarbons released from the rate of hydrocarbons produced to determine the rate of hydrocarbons absorbed by converter  14 .  
         [0028]     Step  56  may be configured to determine a cumulative amount of hydrocarbons absorbed by converter  14 . Specifically, step  56  may functionally relate the rate of hydrocarbons absorbed (d_Absorbed/d_Time), determined in step  54 , and an elapsed time (d_Time) to determine an amount of hydrocarbons absorbed by converter  54 , e.g., an amount of hydrocarbons currently absorbed by converter  14 . Step  56  may combine the currently absorbed amount of hydrocarbons with a previously determined amount of hydrocarbons absorbed, e.g., an amount of hydrocarbons absorbed by converter  14  as determined by controller  18  performing a prior sequence of status logic  30 , to determine the cumulative amount of hydrocarbons absorbed by converter  14 . The determined cumulative amount of hydrocarbons absorbed may be related within step  48  to determine a rate of hydrocarbons released by converter  14 . It is contemplated that an initial amount of hydrocarbons absorbed by converter  14 , e.g., zero, may be assumed when controller  18  performs the first sequence of status logic  30 .  
         [0029]     Step  58  may be configured to compare the rate of hydrocarbons released by converter  14 , as determined in step  48 , with a predetermined value. Step  58  may further be configured to establish status output  60  to indicate a first mode if the rate of hydrocarbons released by converter  14  is greater than a predetermined value. Step  58  may also be configured to establish status output  60  to indicate a second mode if the rate of hydrocarbons released by converter  14  is less than a predetermined value. Specifically, step  58  may include one or more equations configured to functionally relate the determined rate of hydrocarbons released and a predetermined value to determine if the rate of hydrocarbons released to environment  18  is greater than the predetermined value. As such, controller  18  and, in particular status logic  30 , may affect control of engine  12  to operate in at least two modes, a first and a second mode.  
         [0030]     Controller  18  may be configured to control one or more parameters of engine  12  in response to status output  60 . For example, in response to a status output  60  indicative of a first mode, controller  18  may, for example, advance ignition timing, increase the amount of clean exhaust recirculated into engine  12 , operate engine  12  with a lean air-fuel ratio, and/or may vary other operational parameters of engine  12 . Additionally, in response to status output  60  indicative of a second mode, controller  18  may not adjust the operational parameters of engine  12 . As such, engine  12  may, in the first mode, produce less hydrocarbons than that produced by engine  12  in the second mode. Accordingly, status logic  30  may be configured to control engine  12  as a function of a rate of hydrocarbons released to environment  16 . Specifically, control logic  30  may be configured to control engine  12  to produce less hydrocarbons when converter  14  is less capable of absorbing and/or converting hydrocarbons and control engine  12  to produce more hydrocarbons when converter  14  is more capable of absorbing and/or converting hydrocarbons.  
       INDUSTRIAL APPLICABILITY  
       [0031]     The present disclosure provides a system for controlling exhaust emissions and may be applicable to any exhaust system. The disclosed system may absorb and/or convert hydrocarbons within exhaust and may adjust the production of exhaust as a function of the hydrocarbons directed to an environment. The operation of exhaust system  10  will be explained below.  
         [0032]     Exhaust system  10  may be operated at different conditions. For example, engine  12  may be operated in a start-up, idle, shut-down, or at various power, e.g., torque and rotational speed, output conditions. As such, engine  12  may produce exhaust having different properties, such as, for example, temperature or emissions, at different conditions. Additionally, converter  14  may be operated at various conditions as a function of the condition of engine  12 . For example, during a start-up or an idle engine condition, converter  14  may be operating at a cold condition, whereas during a prolonged power output condition, converter  14  may be operating at a warm condition. A cold operational condition of converter  14  may adversely impact the performance of a catalyst therein, e.g., a catalyst may be capable of converting less hydrocarbons at a cold condition than at a warm condition. As such, during operation of converter  14  at cold conditions, an undesirable amount and/or rate of hydrocarbons may released by converter  14  and may be directed to environment  16 . Because converter  14  may not be capable of absorbing and/or converting hydrocarbons as desired, engine  12  may be controlled by controller  18  to produce less hydrocarbons.  
         [0033]     Controller  18  may receive inputs from sensors  20 ,  22 ,  24 ,  26  to monitor the parameters of converter  14  and engine  12 . Specifically, controller  18  may perform status logic  30  to determine a rate of hydrocarbons released by converter  14  and establish an appropriate status output  60  as a function thereof. For example, controller  18  may determine a rate of hydrocarbons released by converter  14  to be greater than a desirable rate. Accordingly, controller  18  may determine a status output  60  configured to adjust the performance of engine  12  to produce less hydrocarbons, e.g., determine status output  60  to indicate a first mode. It is contemplated that controller  18  may be configured to adjust any suitable parameter of engine  12  so as to produce less hydrocarbons, such as, for example, advance ignition timing, retard valve timing, operate engine  12  with a leaner air-fuel ratio, and/or adjust any other parameter.  
         [0034]     Controller  18  may be configured to repeat status logic  30  at any desired frequency, such as, for example, periodically, substantially continuously, and/or at non-uniform cycle times. As such, controller  18  may determine status output  60  as a function of a rate of hydrocarbons released by converter  14 , which may be determined as a function of operational conditions of exhaust system  10  and, in particular, engine  12  and converter  14 . Accordingly, controller  18  may adjust the operation of engine  12  as a function of a rate of hydrocarbons released by converter  14 .  
         [0035]     Because controller  18  determines a rate of hydrocarbons released by converter  14 , engine  12  may be controlled to produce less hydrocarbons when converter  14  is less capable of absorbing and/or converting hydrocarbons. For example, controller  18  may control engine  12  to produce less hydrocarbons when converter  14  and, in particular, a catalyst therein, may be incapable of absorbing and/or converting hydrocarbons from an exhaust as desired. Because controller  18  controls engine  12  as a function of a rate of hydrocarbons released by converter  14 , engine  12  may be more accurately controlled than if controlled in response to a temperature or time sensor configured to indicate when a catalyst may be capable of absorbing and/or converting hydrocarbons as desired. The above disclosure has been described with reference to reducing hydrocarbons generically for clarification purposes and it is contemplated that the present disclosure may be applicable to control any type of hydrocarbons, such as, for example, unburned fuel and/or soluble organic fractions.  
         [0036]     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system for reducing exhaust emissions. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.