Abstract:
A monitoring sub-system coupled to an evaporative emission canister fluidically coupled to a fuel tank and an engine of a machine includes a temperature sensor and a control module coupled to receive sensory output from the temperature sensor. The temperature sensor measures temperature within the evaporative emission canister. The control module is configured to monitor a sorption capacity of the evaporative emission canister based on the received sensory output.

Description:
TECHNICAL FIELD 
       [0001]    The concepts herein generally relate to monitoring evaporative emission control systems in a vehicle, and have particular application to the field of automobile testing. 
       BACKGROUND 
       [0002]    Air pollution is a persistent hazard to human health in most urban areas of the world. Components of air pollution which are hazardous to human health include ozone (which is formed by the combination of hydrocarbons and oxides of nitrogen in sunlight) and toxics (which include particular hydrocarbons such as benzene and 1,3-butadiene). It was recognized in in the 1960s that a major source of hydrocarbons is vehicle emissions and since there has been a regulatory focus on the reduction of hydrocarbon emissions from vehicles. The effort is divided into designing new vehicles to have low emissions through advancing emissions control technology and maintenance of these emissions control systems in-use for the lifetime of the vehicle. The US Environmental Protection Agency estimates that approximately half of vehicle emissions of hydrocarbons are due to the leakage of fuel from vehicles (“evaporative” emissions) versus from un-combusted fuel (“tailpipe” emissions). For this reason, ensuring that evaporative emissions control systems continue to function properly throughout the lifetime of a vehicle is critical to the protection of human health. 
         [0003]    Recognizing the adverse effects that vehicle emissions have on the environment, the 1990 Clean Air Act requires that communities in geographic regions having high levels of air pollution implement Inspection and Maintenance (“I/M”) programs for vehicles in these areas. Such I/M programs are intended to improve air quality by periodically testing the evaporative and exhaust emissions control systems of vehicles and ensuring their proper operation and maintenance. By ensuring that the evaporative and exhaust emissions control systems of vehicles are operational and properly maintained, air pollution resulting from vehicle emissions in the geographic region are drastically reduced. 
         [0004]    In 1992, the California Air Resources Board (CARB) proposed regulations for the monitoring and evaluation of a vehicle&#39;s emissions control system through the use of second-generation on-board diagnostics (“OBDII”). (See California Code of Regulations, Title 13, 1968.1—Malfunction and Diagnostic Systems Requirements—1994 and subsequent model year passenger cars, light-duty trucks, and medium-duty vehicles with feedback fuel control systems.) These regulations were later adopted by the United States Environmental Protection Agency. (See Environmental Protection Agency, 40 C.F.R. Part 86—Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines; Regulations Requiring On-Board Diagnostic Systems on 1994 and Later Model Year Light-Duty Vehicles and Light-Duty Trucks.) The regulations required OBDII systems to be phased in beginning in 1994, and by 1996, almost all light-duty, gasoline-powered motor vehicles in the United States were required to have OBDII systems. Diesel and alternative fuelled vehicles, and medium and heavy duty vehicles were required to have OBDII systems in the years since initial implementation. 
         [0005]    In general, through the use of OBDII systems, the emissions control system of a vehicle is constantly monitored, with a “check engine” light or Malfunction Indicator Light (MIL) on the dashboard of the vehicle being illuminated to indicate a problem with the emissions control system. The OBDII system reduces emissions by indicating an emissions control system malfunction when it occurs so the emissions control system will be repaired, and through interrogation of the OBDII system as part of I/M programs to ensure the emissions control system is functioning properly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram of an evaporative emission control system installed on a fuel tank. 
           [0007]      FIG. 2  is a flow chart illustrating a method of monitoring an evaporative emission canister. 
       
    
    
       [0008]    Many of the features are simplified to better show the features, process steps, and results described herein. 
       DETAILED DESCRIPTION 
       [0009]    OBDII regulations do not require monitoring of the evaporative emission canister, a critical component to the evaporative emission control system. Monitoring of the evaporative emissions canister to identify when the canister is malfunctioning (not capturing the quantity of hydrocarbon vapors as was designed and certified to capture) would identify this source of excess hydrocarbon emissions so that the system could be repaired resulting in significant reductions in hydrocarbon emissions to the environment. The concepts herein relate to determining if the evaporative emissions control canister is malfunctioning. 
         [0010]    One or more of the concepts described in the present disclosure are based on a realization that the evaporative emission canister, a critical component to the evaporative emission control system, typically is not monitored for proper functioning. The evaporative emission canister is filled with a material that adsorbs or absorbs hydrocarbon vapor emanating from the fuel tank while the vehicle is resting, or being refueled and then is purged when the vehicle is operating. If the canister is malfunctioning (that is, no longer effectively capturing hydrocarbons), this situation goes unknown to the vehicle operator, engine/vehicle management computer providing On Board Diagnostics (OBD) or regulatory mandated vehicle emissions inspection personnel. The vehicle would continue to be operated with an undetected malfunction causing high evaporative emissions, impacting ambient air quality and human health. Performance of the evaporative emission canister can degrade over time as dust, particulate, moisture and/or other contaminants foul the hydrocarbon absorbent/adsorbent material. The canister may even be rendered completely inoperable if it is physically damaged, if liquid fuel leaks into the canister from the gas tank and completely saturates the material or if the canister material is not purged as a result of other failed components or a poorly designed purge strategy. As described below, monitoring of an evaporative emission canister can be achieved by observing changes in certain environmental conditions of the canister (e.g., temperature) while the canister is in use under specific circumstances. Such changes in the environmental condition of the canister can be correlated to the capacity of the canister to absorb/adsorb hydrocarbons and therefore changes in absorption/adsorption capacity can be detected. Notably, for convenience of reference, the term “sorption” and related forms of the word are meant to describe both absorption and adsorption interactions. 
         [0011]      FIG. 1  is a diagram of an example evaporative emission control system (“EVAP”)  100  installed on a fuel tank  10 . The evaporative emission control system  100  is adapted to operate within the framework of a motor vehicle (e.g., a car, van, truck, or motorcycle). However, it is appreciated that the concepts described in the present disclosure are not so limited, and can be incorporated in the design of various types of equipment employing internal combustion engines (e.g., stationary engines, air vehicles, marine vehicles, lawn mowers and other types of lawn and garden equipment). Further, while in this example the EVAP  100  is an electronically controlled system, mechanically controlled EVAPs are also well-suited to the concepts described in the present disclosure. 
         [0012]    The EVAP  100  includes an evaporative emission canister (“EVAP canister”)  102  connected to the fuel tank  10  by a fuel tank vent line  104 . The vent line  104  is depicted as a continuous conduit running from an outlet of the fuel tank  10  to an inlet of the EVAP canister  102 . However, it is contemplated that a suitable vent line could include one or more discrete segments connected end-to-end and/or one or more intermediate components (e.g., valves, filters, etc.). The fuel tank  10  includes a fuel storage region  12  for holding liquid volatile fuel  14  (e.g., gasoline) and evaporated fuel vapor  16 . A tank-filler neck  18  spouts outward from the storage region  12  of the fuel tank  10 . The fuel tank  10  is sealed from the surrounding environment by a gas cap  20  sealing the outlet of the tank-filler neck  18 . The sealed gas cap  20  prevents fuel vapors  16  from leaking to the atmosphere through the tank filler neck  18 . 
         [0013]    As the fuel  14  in the storage region  12  of fuel tank  10  evaporates in the heat of the day from a liquid ( 14 ) to a gas ( 16 ), it builds a positive tank pressure. Thus, the fuel tank  10  must be vented to prevent fuel leakage and other complications resulting from the positive pressure. Additionally, as the fuel  14  is consumed by the engine, air must be allowed to enter the fuel tank  10  to prevent complications from a reduction in fuel volume (e.g., collapse under negative pressure and/or fuel pump cavitation). 
         [0014]    The fuel tank vent line  104  and the EVAP canister  102  facilitate venting of the fuel tank  10 . When the fuel tank  10  is under positive pressure from the addition of liquid fuel (“refueling”), increased tank pressure forces fuel vapor  16  to exit the fuel tank  10  via the fuel tank vent line  104 . The fuel vapor  16  is routed by the vent line  104  to the EVAP canister  102 . A fuel vapor sorbent material  106  within the EVAP canister  102  collects the incoming fuel vapor  16  and allows hydrocarbon free air to escape through the air intake/vent  108 . Rapid transfer of fuel vapor  16  from the fuel tank  10  to the EVAP canister  102  during refueling of the vehicle will generally be referred to herein as “loading” the EVAP canister  102  with stored fuel vapors  117 . 
         [0015]    In some examples, the fuel vapor sorbent material  106  is a carbon-based material. For instance, in at least one example, the fuel vapor sorbent material  106  includes activated charcoal. Other suitable fuel vapor sorbent materials can also be used (e.g., an organic polymer compound such as polypropylene). Within the scope of the present disclosure, “fuel vapor sorbent materials” include materials, such as activated carbon/charcoal, that hold fuel vapors and raw hydrocarbons to a surface, as well as materials that diffuse fuel vapors and raw hydrocarbons into itself. 
         [0016]    The EVAP canister  102  includes an air intake/vent  108  controlled by a vent valve  110 . In this example, the vent valve  110  is a normally-open electromagnetic valve (e.g., a solenoid valve). The air intake/vent  108  serves to prevent vacuum pressurization of the fuel tank  10  by allowing air to be drawn through the EVAP canister  102  and vent line  104  to supplement consumed fuel or reductions in vapor volume from cooling. The fresh air intake/vent  108  serves to prevent increased pressurization of the fuel tank during refueling or expansion of fuel vapor  16  by allowing the air which has had the hydrocarbons stripped from it and adsorbed/absorbed to the fuel vapor sorbent material  106  to be vented to the atmosphere. Thus, while the vent valve  110  is open, the EVAP canister  102  and the fuel tank  10  are maintained at atmospheric pressure. As described below, the air intake/vent  108  also facilitates purging of stored fuel vapors  117  from the EVAP canister  102 . 
         [0017]    When the engine is running, stored fuel vapors  117  can be purged from the EVAP canister  102 , and routed via a purge line  112  to the engine&#39;s intake manifold. “Purging” of the EVAP canister  102  is regulated by a purge valve  114 . In this example, the purge valve  114  is a normally closed electromagnetic valve (e.g., a solenoid valve). When the purge valve  114  is opened, the EVAP canister  102  is exposed to the sub-atmospheric pressure of the intake manifold, creating a vacuum effect. The vacuum draws air through the fresh air intake  108  of the EVAP canister  102 . The incoming fresh air flows through the EVAP canister  102 , releasing (or desorbing) the fuel vapors  117  from the fuel vapor sorbent material  106 . The air and released fuel vapors  117  are routed to the intake manifold by the purge line  112 , and mixed with the primary sources of air and fuel. The combined sources of air and fuel are ultimately provided to the engine cylinders for combustion. 
         [0018]    A control module  116  operates the vent valve  110  and the purge valve  114 . The control module  116  is depicted schematically in  FIG. 1  as a stand-alone electronic control unit (ECU). However, as a practical matter, the control module  116  may be incorporated within a more robust ECU, such as the powertrain control module (PCM) or the engine control module (ECM) of a motor vehicle. Alternatively, the control module  116  could be distributed across multiple ECUs. 
         [0019]    Purge valve  114 , is modulated between closed and open by the control module  116  at a frequency appropriate to facilitate purging of the EVAP canister  102 . In some examples, the control module  116  is programmed to purge the EVAP canister in response to certain vehicle operating conditions (e.g., some combination of engine temperature, speed, and load). Numerous strategies are known for controlling the purge valve  114 . All suitable purge control strategies and algorithms are contemplated within the scope of the present disclosure. 
         [0020]    The EVAP  100  includes a monitoring sub-system designed to estimate the sorption capacity of the EVAP canister  102 . The monitoring sub-system includes a first temperature sensor  120  measuring temperature within the EVAP canister  102 , and a second temperature sensor  122  measuring temperature of ambient air, each of which is connected to the control module  116 . The temperature sensors  120  and  122  can be any type of sensor, including electro-mechanical, resistive, or electronic sensors, including those based on physical contact or convection and radiation temperature measurement principles. In some examples, the temperature sensors  120  and  122  are thermistors. 
         [0021]    In one example, the temperature sensor  120  includes a single sensor placed within or otherwise positioned to measure temperature within the EVAP canister  102 . The temperature sensor  120  thus measures the temperature of the material  106  within the canister  102 . In certain instances, the single sensor is designed to measure the temperature at a single key point within the EVAP canister  102 . For instance, the single sensor may be positioned near the inlet of the EVAP canister  102  (at the port opening to the fuel tank vent line  104 ) or near the outlets of the EVAP canister  102  (at the port opening to the purge line  112  or the air intake/vent line  108 ). In another example, the temperature sensor  120  includes more than one temperature sensor positioned to measure at different locations throughout the EVAP canister  102 . The multiple temperature sensors can provide a temperature profile and/or an average temperature of the EVAP canister  102 . The temperature sensor  122  can be a conventional outside air temperature (OAT) sensor mounted outside the passenger compartment of the vehicle, or any other type of temperature sensor. 
         [0022]    The control module  116  receives sensory output from each of the temperature sensors  120  and  122 , and compares the actual temperature within the EVAP canister  102  (as reflected by sensory output from the temperature sensor  120 ) to the ambient temperature (as reflected by sensory output from the temperature sensor  122 ) to establish a relative temperature of the EVAP canister  102 . In certain instances, the control module  116  receives sensory output from the fuel quantity sensor  21  and can determine the amount of vapors passed through the EVAP canister  102  during the loading operations based on the change in the amount of fuel in the fuel tank  10 . In certain instances, the control module  116  receives sensory output from the purge flow meter  115  and can determine the amount of vapors passed through the EVAP canister  102  during the purge operations based on the flow rate of the vapors passed through the purge line  112  and the characteristics of the purge line  112 . As described below, the control module  116  determines the sorption capacity of the EVAP canister  102  by monitoring the relative temperature of the EVAP canister  102  and the amount of vapors passed through the EVAP canister  102  during the periodic loading and purging operations. As used herein “sorption capacity” refers the total mass of fuel vapor/raw hydrocarbons that can be releasably captured (either absorbed or adsorbed) by the EVAP canister  102 . 
         [0023]    The magnitude of the change in temperature of the sorbent material  106  via the temperature sensor(s)  120  during loading or purging is used to determine the sorption capacity of the sorbent material  106 . As one example, sorption of the fuel vapors  16  onto surfaces of the sorbent material  106  produces heat as a by-product of the phase change of the fuel vapors. Thus, during loading, the relative temperature of the sorbent material  106  increases in proportion to the amount of fuel vapor absorbed/adsorbed. Likewise, during purging, the relative temperature of the sorbent material  106  decreases in proportion to the amount of fuel vapor desorbed. 
         [0024]    The relationship between the magnitude of change in temperature and the sorption/desorption of fuel may depend on numerous factors, including canister geometry, fuel type, ambient temperature, fuel vapor temperature  22  and composition of the sorption material. The sorption capacity of the sorbent material  106  corresponds to the magnitude of temperature increase and decrease during loading and purging respectively, and the amount of vapors passed through the canister. 
         [0025]    In some examples, a correlation based on empirical data can be used to convert the observed increase or decrease in temperature within the EVAP canister  102  to a value representing sorption capacity. The correlation can be provided in the form of an empirical formula executed by the processor of the control module  116 , or in the form of a look-up table stored in the memory of the control module  116 . To determine if the EVAP canister  102  is functioning properly (the sorbent material can adsorb/absorb sufficient hydrocarbons to allow the vehicle to pass a certification or an in-use evaporative emissions compliance test), the control module  116  can compare a recently calculated sorption capacity to a predetermined threshold value. If the calculated sorption capacity is greater than the threshold value, the EVAP canister  102  is deemed to be functioning properly. If the computed sorption capacity is less than the threshold value, the EVAP canister  102  is deemed to be malfunctioning. 
         [0026]    In some examples, the control module  116  is programmed to determine whether the EVAP canister  102  is malfunctioning by directly observing the magnitude of temperature change of the sorbent material  106 , for a given amount of vapors, during loading or purging. In such examples, the control module  116  is pre-programmed with threshold values of temperature change or rate of change applicable during loading and purging respectively, for different conditions. The threshold values correspond to an acceptable sorption capacity of the EVAP canister  102 . Thus, for example, when the magnitude of temperature increases within the EVAP canister  102  during loading is below a threshold value stored in memory of the control module  116 , the EVAP canister is deemed to be malfunctioning. 
         [0027]    In some examples, the threshold value for sorption capacity is a function of the amount of fuel ( 14 ) added to the fuel tank  10  as determined by a fuel quantity sender unit  21  and the control module  116 . When fuel ( 14 ) is added to the fuel tank  10 , fuel vapors  16  are displaced and pushed into the EVAP canister  102 . The amount of fuel vapor  16  loaded into the EVAP canister  102  is proportional to the amount of added fuel ( 14 ) as determined by the fuel quantity sender unit  21  and the control module  116 . The threshold value for sorption capacity can be calculated based on the magnitude of temperature change of the sorbent material  106 , the amount of fuel vapor  16  loaded into the EVAP canister  102  and other factors such as ambient temperature. 
         [0028]    In some examples, the threshold value for sorption capacity is a function of the amount of vapors exhausted through the purge line  112  as determined by the purge flow meter  115  and the control module  116 . The amount of vapors purged from the EVAP canister  102  can be determined from the flow rate through the purge line  112 , as measured by the purge flow meter  115 , the cross-sectional area of the purge line  112  and the temperature. The threshold value for sorption capacity can be calculated based on the magnitude of temperature change of the sorbent material  106 , the amount of fuel vapor purged from the EVAP canister  102  through the purge line  112  and other factors. 
         [0029]    In some examples, if the control module  116  determines that the EVAP canister  102  is malfunctioning, an indication light (e.g., the malfunction indicator light) is illuminated to indicate there is a problem with the evaporative emissions control system and a diagnostic trouble code (DTC) is set by the OBDII system to inform technicians of the problem. The determination may be part of the evaporative emissions control system monitoring as part of OBDII. In some examples, the control module  116  may alter the purge strategies for relieving the EVAP canister  102  in response to determining that the canister is malfunctioning. For example, if the EVAP canister  102  is not absorbing/adsorbing a sufficient amount of hydrocarbons from the fuel vapors  16 , the control module  116  may open the purge valve  114  more frequently and/or for a longer duration. Other ECUs on the motor vehicle may also receive a signal indicating that the EVAP canister  102  is malfunctioning and appropriately alter other vehicle operations. For example, the ECM may alter the stoichiometry of the air-fuel mixture to accommodate for the decrease in fuel vapors recovered from the malfunctioning EVAP canister  102 . 
         [0030]      FIG. 2  is a flow chart illustrating a method  200  of monitoring an evaporative emission canister. The method  200  can be implemented, for example, in connection with the EVAP system  100  shown in  FIG. 1 . At operation  202 , the temperature within the EVAP canister is determined. For example, one or more sensors positioned within the EVAP canister can measure the interior temperature and provide sensory output to the control module. In certain instances, an outside air temperature sensor can be used to measure an ambient temperature and provide sensory output to the control module. The control module can compare the ambient temperature to the actual temperature of the EVAP canister to determine a relative temperature. At operation  204 , the control module, knowing the amount of vapors loaded or purged from the EVAP canister from a fuel quantity sensor or a purge flow meter, compares the EVAP canister temperature (relative or absolute) before and after refueling or a purge event, and determines the sorption capacity of the EVAP canister. In some examples, the control module alternately or additionally monitors a rate of change in temperature of the EVAP canister during loading and/or purging operations to determine the sorption capacity. At operation  206 , the control module determines if the EVAP canister is functioning properly based on its sorption capacity. 
         [0031]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made.