Abstract:
A method and system for testing an evaporative emission control system for leaks. The method begins by setting a variable reference orifice to a preselected diameter. Then, a vacuum pump evacuates a reference volume in the vicinity of the variable reference orifice. The reference volume is defined by the vacuum pump, and the reference orifice. Then, after a specified evacuation time, the method determines a pressure in the reference volume. That pressure is stored as the threshold test value. The method continues by evacuating the entire EVAP system for a predetermined time. A leak can then be identified if after the evacuation, the system pressure falls at least to the threshold test value. Switching the vacuum pump between the first and second positions is accomplished with a changeover valve having parallel airways configured for evacuating a small volume to the reference orifice and also evacuating the entire EVAP system.

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure generally relate to Evaporative Emission Control Systems (EVAP) for automotive vehicles, and, more specifically, to detecting leaks within EVAP systems. 
     BACKGROUND 
     Gasoline, the fuel for many automotive vehicles, is a volatile liquid subject to potentially rapid evaporation, in response to diurnal variations in the ambient temperature. Thus, the fuel contained in automobile gas tanks presents a major source of potential emission of hydrocarbons into the atmosphere. Such emissions from vehicles are termed ‘evaporative emissions’, and those vapors can be emitted vapors even when the engine is not running. 
     In response to this problem, industry has incorporated evaporative emission control systems (EVAP) into automobiles, to prevent fuel vapor from being discharged into the atmosphere. EVAP systems include a canister (the carbon canister) containing adsorbent carbon) that traps fuel vapor. Periodically, a purge cycle feeds the captured vapor to the intake manifold for combustion, thus reducing evaporative emissions. 
     Hybrid electric vehicles, including plug-in hybrid electric vehicles (HEV&#39;s or PHEV&#39;s), pose a particular problem for effectively controlling evaporative emissions. Although hybrid vehicles have been proposed and introduced in a number of forms, these designs all provide a combustion engine as backup to an electric motor. Primary power is provided by the electric motor, and careful attention to charging cycles can produce an operating profile in which the engine is only run for short periods. Systems in which the engine is only operated once or twice every few weeks are not uncommon. Purging the carbon canister can only occur when the engine is running, of course, and if the canister is not purged, the carbon pellets can become saturated, after which hydrocarbons will escape to the atmosphere, causing pollution. 
     EVAP systems are generally sealed to prevent the escape of any hydrocarbons. These systems require periodic leak detection tests to identify potential problems. 
     A requirement for leak testing, of course, is a standard against which to measure. In general, leak standards are expressed in terms of the maximum allowable orifice size. This field is relatively new, however, and regulatory bodies often change standards, requiring adaptation of standard leak detection procedures. Such changes often necessitate modifications in the measuring equipment, which imposes higher costs. One aspect under considerable discussion is the maximum allowable orifice size—that is, size limit for the largest allowable leak. Commonly used test equipment provides a reference orifice to establish a reference pressure level and thus any change in the maximum allowable orifice size would require changes in the reference orifice as well. 
     Understandably, changes to test systems, such as modifications to the orifice size, exact a toll on the manufacturers and service providers. This leaves alternatives to accommodate multiple orifices or attempts to determine the reference pressure efficiently during EVAP leak tests substantially unchallenged. 
     SUMMARY 
     One aspect of the present disclosure describes a method for testing an evaporative emission control system for leaks. The method begins by setting a variable reference orifice to a preselected diameter. Then, a vacuum pump evacuates a reference volume in the vicinity of the variable reference orifice. The reference volume is defined by the vacuum pump, the reference orifice, and fluid communication lines associated with those devices. Then, at the end of a specified evacuation time, the method determines a pressure in the reference volume. That pressure is stored as the threshold test value. The method continues by evacuating the entire EVAP system for a predetermined time. A leak can then be identified if after the evacuation, the system pressure falls at least to the threshold test value. 
     Another aspect of the present disclosure is in evaporative leak check system. One component of the system is at least one passage facilitating fluid communication between the outside atmosphere and the system interior. A vacuum pump is positioned in fluid communication with the passage and configured to carry out evacuating operations based on a first position and a second position. The first vacuum pump position facilitates determination of a reference pressure value or a pressure threshold value, and the second vacuum pump position facilitates determination of a system pressure value. A changeover valve switches between the first position and the second position. A a servo controlled variable reference orifice facilitates determination of the pressure threshold value. 
     Additional aspects, advantages, features and objects of the present disclosure are apparent from the drawings and the detailed description of the illustrative embodiments construed in conjunction with the appended claims that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures described below set out and illustrate a number of exemplary embodiments of the disclosure. Throughout the drawings, like reference numerals refer to identical or functionally similar elements. The drawings are illustrative in nature and are not drawn to scale. 
         FIG. 1A  is a schematic view of an exemplary EVAP system installed in a PHEV, incorporated with a conventional ELCM. 
         FIGS. 1B, 1C, and 1D , are schematics describing the working of an exemplary ELCM. 
         FIG. 2  is a schematic of an ELCM according to the present disclosure. 
         FIG. 3  is a flowchart illustrating an exemplary method to carry out an EVAP leak diagnosis in vehicles, according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is made with reference to the figures. Exemplary embodiments are described to illustrate the subject matter of the disclosure, not to limit its scope, which is defined by the appended claims. 
     Overview 
     In general, the present disclosure describes a method for determining EVAP leaks in PHEVs via a variably configured orifice arrangement. To this end, a servo valve having a position interface is installed, into which, an operator can dial-in a required orifice or a passage size. In response, the servo valve replicates a conventional orifice having a corresponding diameter. Leak tests commence thereafter. 
     Exemplary Embodiments 
     The following detailed description illustrates aspects of the disclosure and its implementation. This description should not be understood as defining or limiting the scope of the present disclosure, however, such definition or limitation being solely contained in the claims appended hereto. Although the best mode of carrying out the invention has been disclosed, those in the art would recognize that other embodiments for carrying out or practicing the invention are also possible. 
       FIG. 1A  illustrates a conventional evaporative emissions control system  100 . As seen there, the system  100  is made up primarily of the fuel tank  102 , a carbon canister  110 , and the engine intake manifold  130 , all operably connected by lines and valves  105 . It will be understood that many variations on this busy design are possible, but the illustrated embodiment follows the general practice of the art. It will be understood that the system  100  is generally sealed, with no open vent to atmosphere. 
     Fuel tank  102  is partially filled with liquid fuel  105 , but a portion of the liquid evaporates over time, producing fuel vapor  107  in the upper portion (or “vapor dome  103 ”) of the tank. The amount of vapor produced will depend upon a number of environmental variables, such as the ambient temperature. Of these factors, temperature is probably the most important, given the temperature variation produced in the typical diurnal temperature cycle. For vehicles in a sunny climate, particularly a hot, sunny climate, the heat produced by leaving a vehicle standing in direct sunlight can produce very high pressure within the vapor dome  103  of the tank  102 . A fuel tank pressure transducer (FTPT)  106  monitors the pressure in the fuel tank vapor dome  103 . 
     Vapor lines  124  operably join various components of the system. One, line  124   a , runs from the fuel tank  102  to carbon canister  110 . A normally closed fuel tank isolation valve (FTIV)  118  regulates the flow of vapor from fuel tank  102  to the carbon canister  110 , so that flows normally freely permitted, so that the carbon pellets can adsorb the vapor generated by evaporating fuel. Vapor line  124   b  joins line  124   a  in a T intersection beyond FTIV  118 , connecting that line with a normally closed canister purge valve (CPV)  126 . Line  124   c  continues from CPV  126  to the engine intake manifold  130 . CPV  126  is controlled by signals from the powertrain control module (PCM)  122 , which also controls FTIV  118 . 
     Canister  110  is connected to ambient atmosphere at vent  115 , through a normally closed canister vent valve (CPV)  114 . Vapor line  124   d  connects that  115  in canister  110 . 
     Powertrain Control Module (PCM  122 ) may include a controller (not shown) of a known type connected both sensors, such as FTPT  106 , as well as active control components, such as CCV  114 . Connections may carry to other sensors as well. The controller may be of a known type, forming one part of the hardware of the said system, and may be a microprocessor based device that includes a central processing unit (CPU) for processing incoming signals from known source. The controller may be provided with volatile memory units, such as a RAM and/or ROM that function along with associated input and output buses. Further, the controller may also be optionally configured as an application specific integrated circuit, or may be formed through other logic devices that are well known to the skilled in the art. More particularly, the controller may be formed either as a portion of an existing electronic controller, or may be configured as a stand-alone entity. 
     During normal operation, FTIV  118 , CPV  126 , and CVV  114  are all closed. That configuration retains vapor within the fuel tank  102 . Periodically, FTIV  118  is opened, allowing vapor to flow into canister  110 . There, carbon pellets can adsorb fuel vapor. 
     To purge the canister  110 , FTIV  118  is closed, and valves  126  and  114  are opened. It should be understood that this operation is only performed when the engine is running, which produces a vacuum at intake manifold  130 . That vacuum causes an airflow from ambient atmosphere through vent  115 , canister  110 , and CPV  126 , and then onward into the intake manifold  130 . As the airflow passes through canister  110 , it entrains fuel vapor from the carbon pellets. The fuel vapor mixture then proceeds to the engine, where it is mixed with the primary fuel/air flow to the engine for combustion. 
     Evacuation Level Check Monitor (ELCM  140 ), is typically installed near the vent  115 , and is operably connected to the PCM  122 . Other arrangements may be contemplated. ELCM  140  can be a component available and known to the art for performing EVAP leak checks, such as the ELCM manufactured by Denso Corporation™. A detailed ELCM layout and working principle is set out in  FIGS. 1B, 1C, and 1D . That layout includes a vacuum pump  142 , an absolute pressure sensor  144 , a Changeover Valve (COV  146 ), and a reference orifice  148 . Vacuum pump  142  evacuates the EVAP system for leak testing, under control of PCM  122 . 
       FIGS. 1B, 1C, and 1D  schematically illustrate ELCM  140 . This device includes two input/output connections. The first connects to fluid communication line  124   d , which runs to canister  110 . A second connection provides a vent to atmosphere through system vent  115 . Within the device, three possible airflow paths are provided, as selected by a solenoid  302 . That device has a solenoid body  301 , a generally cylindrical body having two flow paths formed through it: a vertically oblique path and a horizontal path. Solenoid  302  moves between a de-energized position, illustrated in  FIG. 1B , in which solenoid body  301  extends to a maximum extent downward into ELCM  140 , and an energized position, seen in  FIG. 3B . In the latter position, solenoid body  301  is drawn upward toward the windings of solenoid  302 . 
     Of the flow paths within ELCM  140 , airflow path  111   a  extends from a position adjacent solenoid  302  to system vent  310 . This airflow path is positioned in alignment with one outlet of the oblique flow path when solenoid  302  is not energized. 
     Airflow path  111   b  runs from the junction with fluid communication line  318 , to a junction with airflow path  111   a . This flow path is interrupted by solenoid  302 , and the ends thus formed in flow path  111   b  are positioned in alignment with the horizontal path when solenoid  302  is energized. Additionally, a three-way valve  303  is positioned in flow path  111   b  between solenoid  302  and the junction with path  111   a . Valve  303  can be open, closed, or placed in fluid flow with pump  142 . 
     Airflow path  111   c  has a general U-shape, straddling solenoid body  301 , with both ends opening onto airflow path  111   b  on both sides of solenoid body  301 . An orifice  148 , having a size that can be selected to accommodate various regulatory requirements, such as 0.020″, is inserted into flow path  111   c.    
     In the de-energized state shown in  FIG. 1B , the oblique path joins flow path  111   a  and  111   b . In a situation in which CPV  122  is closed, operation of pump  157 , together with the positioning of valve  303  to connect pump  142  to flow path  111   b , routes the airflow through orifice  148 . 
     The energized state of solenoid  302 , shown in  FIG. 1D , pulls solenoid body  301  upward, so that the horizontal path completes the straight-through channel of path  111   b . When valve  303  is open, airflow path  111   b  provides a ready flow path to atmosphere. 
     The purpose of reference orifice  148  is to simulate the effect of a leak having exactly the same size as the reference orifice. When the system is evacuated through a reference orifice, the resulting vacuum level represents the level that can be achieved with a leak having the size of the reference orifice in the system. Thus, if the maximum allowable orifice size for a given regulatory jurisdiction is 0.020″, then evacuating the system through the reference orifice will establish a reference vacuum level. As noted, frequent changes in EVAP leak regulations lead to costly modifications to standard testing procedures. Here, the orifice holds maximum potential for a change. 
     Turning to  FIG. 2 , an exemplary embodiment of the present disclosure describes a variable reference orifice  248 , size-controlled by a servomechanism. In principle, a servomotor provides a positional control capability to an operator, thereby varying the orifice size as demanded by the applicable standards. Other valve types, however, that apply hydraulic, pneumatic, or magnetic principles, are available, and thus, may be employed. 
     COV  246 , vacuum pump  242 , and pressure sensor  244  operate as described above. The reference orifice  248  employed here, however, may be set to a number of different orifice sizes. A servo control system  250 , selected from those known and available to the art, allows an operator to set the reference orifice size. 
       FIG. 3  sets out a method  300  for implementing EVAP system leak detection using a variable orifice. At a first step  302 , an operator may set a variable reference orifice to a preselected diameter, employing a suitable interface. That preselect diameter varies according to applicable regulatory requirements. Other factors, known to those in the art, may necessitate other variations. It should be noted that this step may occur before the vehicle is sold, either at the assembly plant or at a dealer&#39;s maintenance facility. A first setting can be employed at the time the vehicle is manufactured or sold, with the orifice setting based upon regulations in force at that time. If regulations change at some point after that, the orifice size can be changed easily and conveniently by a service technician. 
     Next, at step  304 , the vacuum pump  242  evacuates a reference volume in the variable reference orifice&#39;s vicinity. In the illustrated embodiment, ELCM  240  provides a readily accessible and reasonably sized reference volume for evacuation. The evacuation is carried on for a predetermined time, drawing and through the reference orifice  248  to simulate a leak at the same size. 
     At step  306 , the pressure sensor  244  senses the pressure within the reference volume and feeds that to PCM  122 . In a following step  308 , the PCM  122  stores that information as the reference threshold value. 
     Then, PCM  122  initiates the full leak test, starting by energizing the COV  246 . The solenoid  302  activates, pulling solenoid body  301  upward (arrow A,  FIG. 1D ) to establish a direct passage between the system&#39;s interior and outside atmosphere. Then, FTIV  118  and CCV  114  are opened, so that the entire EVAP system is subject to evacuation. CPV  126  remains closed, but the canister  110  and fuel tank  102  and associated communication lines are evacuated 
     The evaluation cycle requires about two to 15 minutes for the vacuum level to stabilize. Once stable vacuum is reached, PCM  122  compares the attained vacuum level against the vacuum level when the reference check was performed. If any system leaks do not aggregate to the sized to which the variable reference orifice  248  is set, then pressure level at the end of the evacuation cycle will be at or below the reference level. Failure to achieve the reference level indicates the presence of a leak greater than the size of the reference orifice . . . . 
     Differing configurations of the system  100  may not restrict the disclosed ELCM&#39;s usability as through known mechanisms someone skilled in the art may form embodiments apart from those described. In effect, despite the system&#39;s customization and/or variation to any known extent, those skilled in art can ascertain ways to incorporate the servo control mechanism, described so far, into ELCM  240 . Similarly, variations to the ELCM  240  may be contemplated. 
     The discussed system  100  may be applied to a variety of other applications as well. For example, any similar application, requiring the adherence to stringent emission norms may make use of the disclosed subject matter. Accordingly, it may be well known to those in the art that the description of the present disclosure may be applicable to a variety of other environments as well, and thus, the environment disclosed here must be viewed as being purely exemplary in nature. 
     Further, the system  100  discussed so far is not limited to the disclosed embodiments alone, as those skilled in the art may ascertain multiple embodiments, variations, and alterations, to what has been described. Accordingly, none of the embodiments disclosed herein need to be viewed as being strictly restricted to the structure, configuration, and arrangement alone. Moreover, certain components described in the application may function independently of each other as well, and thus none of the implementations needs to be seen as limiting in any way. 
     Accordingly, those skilled in the art will understand that variations in these embodiments will naturally occur in the course of embodying the subject matter of the disclosure in specific implementations and environments. It will further be understood that such variations will fall within the scope of the disclosure. Neither those possible variations nor the specific examples disclosed above are set out to limit the scope of the disclosure. Rather, the scope of claimed subject matter is defined solely by the claims set out below.