Abstract:
A sealed housing evaporative determination (SHED) apparatus and method for practically zero emission vehicles (PZEV) provides periodic sampling of ambient air within a substantially air-tight testing structure enclosing a vehicle under test. Pressure drops within the testing structure are compensated by injecting air substantially free of hydrocarbons into the testing structure. Pressure increases within the testing structure are reduced by withdrawing ambient air from the testing structure. Hydrocarbon content of any withdrawn ambient air is determined from the latest sample, and cumulative evaporative emissions are adjusted accordingly.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to motor vehicle emissions testing and, more particularly, to a computer controlled sealed housing evaporative determination (SHED) testing apparatus and method for automatically testing motor vehicle evaporative emissions for practically zero emission vehicles (PZEV) under a number of testing schedules.  
         [0002]     In addition to commonly known tailpipe exhaust emissions produced during engine operation, there are also evaporative emissions which are generated while the vehicle is simply sitting parked. Testing for evaporative emissions is typically conducted according to what is commonly known as a sealed housing evaporative determination (SHED) test.  
         [0003]     Modern regulations require measuring evaporative emissions produced by a vehicle over the course of several days and in response to changing temperature conditions. However, changes in air temperature cause corresponding changes in the volume and hence changes in the pressure of the ambient air within the SHED structure. Pressure differences between the interior and the ambient air of the SHED structure and the outside environment encourage migration of air either into or out of the testing structure through any leaks, thus affecting the accuracy of the test results. Therefore, it is desirable to control the pressure changes in order to maintain a pressure difference between the interior of the SHED structure and the surrounding outside atmosphere as near zero as possible.  
         [0004]     One known approach to performing variable temperature SHED tests while controlling the pressure differential is set forth in U.S. Pat. No. 5,592,372. While the apparatus and methods disclosed by the &#39;372 patent are suitable for emission testing on standard vehicles, new approaches are now required for PZEV testing, because the levels of hydrocarbons being monitored are much lower than those of standard vehicles. PZEV testing additionally requires a breakdown of the components of the hydrocarbons being emitted to determine the source of the emissions—e.g. refrigerant from the air conditioning system versus fuel vapor from the fueling system.  
         [0005]     Hence, there is seen to be a need for SHED testing of PZEV&#39;s wherein the evaporative emission levels being monitored are substantially lower than for standard vehicles tested under previous arrangements.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with one aspect of the invention, a system for testing motor vehicle evaporative emissions includes a substantially air-tight testing structure adapted for enclosing a motor vehicle under test, the testing structure containing a known volume of ambient interior air. A sampling mechanism for periodically measuring and analyzing component parts of hydrocarbons in a sample of the ambient interior air is coupled to the testing structure. A pressure measuring mechanism for indicating a pressure differential between the ambient interior air of the testing structure and atmosphere outside of the testing structure is operative to enable an injector element to inject air containing substantially zero hydrocarbons into the testing structure whenever the pressure of the atmosphere outside of the testing structure is higher than the pressure of the ambient interior air by a preselected differential. The pressure measuring mechanism is likewise operative to enable an exhaling element to withdraw interior ambient air from the testing structure whenever the pressure of the ambient air interior to the structure is higher than the pressure of the atmosphere outside of the structure by a predetermined differential. A flow measuring and calculating element determines in conjunction with a most recent sample from the sampling mechanism an amount of hydrocarbon exhaled from the testing structure whenever the exhaling element is withdrawing interior ambient air from the testing structure.  
         [0007]     In another aspect of the invention, a method for determining evaporative emissions of a motor vehicle over a predetermined test time interval includes enclosing a subject motor vehicle in a substantially air-tight testing structure containing a known volume of ambient interior air, periodically sampling during the test time interval the ambient interior air for hydrocarbon content and maintaining a running count of the hydrocarbon content. A pressure differential between the ambient interior air and atmosphere outside of the testing structure is monitored, and air containing substantially zero hydrocarbons is injected into the testing structure whenever the pressure differential indicates atmospheric pressure outside the testing structure exceeds internal ambient air pressure by a preselected amount. Interior ambient air from the testing structure is withdrawn therefrom whenever the pressure differential indicates internal ambient air pressure exceeds atmospheric pressure outside the testing structure by a preselected amount. An amount of hydrocarbons withdrawn from the testing structure is determined for any given sample and the running count of the hydrocarbons emitted is adjusted accordingly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     The objects and features of the invention will become apparent from a reading of a detailed description, taken in conjunction with the drawing, in which:  
         [0009]      FIG. 1  is a block diagram of a sampling and calibration system for SHED testing arranged in accordance with the principles of the invention;  
         [0010]      FIG. 2  is a flow chart of an exemplary method of determining evaporative vehicular emissions in accordance with the principles of the invention; and  
         [0011]      FIG. 3  is a flow chart showing further details of adjusting a total emission level to account for any withdrawal of ambient air from the testing structure of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]      FIG. 1  sets forth the block diagram of an arrangement for use with a substantially air-tight testing structure for monitoring evaporative emissions from vehicles while in a non-running condition. The vehicle under test (not shown) is placed within the testing structure having a wall  169  through which periodic air sampling is performed.  
         [0013]     A heated air sampling line or conduit  173  extends via valve  106  through testing structure wall  169  and then through another control valve  103   c  to a sampling probe for inside ambient air of the testing structure. Additional specific locations associated with the vehicle under test may be sampled via probes  102  and  101  respectively coupled to the sampling conduit via control valves  103   b  and  103   a.    
         [0014]     A source  133  of substantially zero hydrocarbon containing air is coupled to the interior of the testing structure via wall  169  through regulator valve  107 , ball valve  109  and control valves  104  and  105 . The pressure of this zero HC air is monitored via gauge  108 . As will be explained in more detail below, zero hydrocarbon air is introduced into the testing structure via wall  169  whenever inside ambient air has been bled off to bring the pressure differential between the outside atmosphere and the interior of the testing structure substantially to zero.  
         [0015]     Heated sampling conduit  173  terminates at a micro-metering needle valve  114  and a bellows pump  115 , in turn coupled to a flame ionization detector (FID)  116  which measures the total hydrocarbon content of a sample. Heated conduit  173  additionally is coupled to a gas analyzer  127  for analysis of the specific types of hydrocarbons present in the sample. Analyzer  127  preferably comprises an Innova model 3433 photoacoustic gas analyzer.  
         [0016]     FID  116  is coupled to a fuel source  123  via a regulator valve  122  and the pressure in the fuel line is monitored by gauge  121 . Additionally, FID  116  is coupled via path  118  to a flow meter  119  and then via valve  120  to a Return-to-SHED line  124  and a dump  125 .  
         [0017]     Analyzer  127  is coupled via path  128  and flow meter  126  to control valve  120  for access to dump  125  or RTS  124 . An air input  129  of analyzer  127  feeds a source of zero hydrocarbon air  133  via regulator  132  and flow meter  130  to analyzer  127  for providing purge air thereto. A front panel access air source  134  is also provided for diagnostic purposes. Zero hydrocarbon air is input to FID  116  via path  117  for enabling the combustion process of the flame of FID  116 .  
         [0018]     Arrangement  100  advantageously utilizes a spill-over cal-through sampling system. A sample is taken every predetermined period, for example ten minutes, and the hydrocarbon content of emissions within testing structure defined by wall  169  is then periodically updated. FID  116  is likewise periodically calibrated via a spill-over arrangement comprising conduit  168  flowing through a control valve  113  past an end of heated conduit  173 , then through control valve  110  and flow meter  174  to dump  112 . A preselected level of hydrocarbon content is derived from various supplies of propane for calibration purposes. These supplies  156 ,  158 ,  160 ,  162 , and  164  respectively provide propane with known levels of hydrocarbon content for the calibration procedure. Additionally, a source of zero hydrocarbon air  166  is made available to the calibration spillover pathway. The calibration gas sources are controlled via solenoid valves  155 ,  157 ,  159 ,  161 ,  163  and  165 . The calibration source then proceeds through regulator valve  153  and control valve  152  through a flow meter  151  to path  168 . Control valves  110  and  113  are closed during the normal sampling routine but are open for the calibration. Valve  106  would then be closed during calibration. Back-flow and contamination of the calibration gas sources are prevented via check valves  167   a - f  associated respectively with the zero hydrocarbon air source  165  and propane sources control valves  163 ,  161 ,  159 , 157  and  155 .  
         [0019]     The pressure differential between the outside atmosphere and the inside ambient air of the testing structure is determined by a Dwyer magnahelic water column gauge  149  with an electrical output which is utilized to actuate valve  142  to enable the testing structure to “exhale” so as to bring the pressure differential down substantially to zero. Barometer  148  also monitors ambient atmosphere external to the testing structure and pressure transducer  150  is used to monitor pressure of fuel tank  172 .  
         [0020]     The volume of interior ambient air which is exhaled via ball valve  142  is determined using a laminar flow element  138  with pressure probes  183  and  184  at opposite ends thereof. The pressure differential across the laminar flow element is then monitored via pressure transducer  139  coupled via leads  140  and  141  to probes  183  and  184 . A processor based controller  180  is coupled to the various elements of  FIG. 1  via a data distribution and collection bus  182  and via a control bus  181 . When the amount of exhaled air is to be determined by controller  180 , the controller  180  uses transducer  139  to determine the pressure differential across the laminar flow element  138  which in turn enables the computer to derive the flow rate at the time of exhale. The hydrocarbon content in the ambient air sample from the latest sample times the volume of air exhaled is used to derive the hydrocarbon content of the air which was exhaled. This amount is then used to adjust the running total being maintained at controller  180 .  
         [0021]     When a predetermined unacceptable pressure differential is detected by gauge  149 , valve  144  is opened and shop air at supply  147  via regulator valve  145  is directed to ball valve  142  to open same for enabling air to exit from the interior of the testing structure via wall  169 .  
         [0022]     Blocks  135 ,  136  and  137  of  FIG. 1  set forth three alternative approaches to performing “retention testing” of the test structure, which basically is a measurement of the air tightness of that structure. In a retention test, a known quantity of propane is introduced into the sealed test structure. After a cycle time, for example, twenty-four hours, the introduced hydrocarbons are measured and a preordained amount of hydrocarbon must remain within the testing structure for it to be certified. The known amount of hydrocarbons is introduced via one of the three approaches set forth in blocks  135 ,  136 , and  137 . Blocks  135  and  137  present alternate approaches to gravimetric propane injection for retention testing—a preferred injection method for this invention. A gravimetric hydrocarbon injection device is basically a small cylinder hooked up to pure propane and coupled to a hole in the side of the wall  169 . Once the propane is injected, the cylinder is weighed to determine precisely how much propane was injected. Block  135  injects gravimetrically via a manually operated valve, while block  137  utilizes a quick-connect coupling. Of course, the injection hole is capped when not in use.  
         [0023]     Alternatively, to gravimetric coupling, one could use a critical flow orifice in wall  169 , as represented by block  136 .  
         [0024]     An advantage of the previously discussed periodic calibration of FID  116  is that, since the calibration gas from sources  156 ,  158 ,  160 , 162 ,  164  or  166  is introduced past an end of conduit  173 , the calibration gas also flows through heated conduit  173 . Therefore, any contamination in sample conduit  173  or the valves associated therewith is taken into account when calibrating FID  116 .  
         [0025]     An additional improvement attained with the invention is the use of substantially zero hydrocarbon air as an “inhale” source whenever the pressure of the outside atmosphere exceeds that of the interior ambient air of the testing structure by a predetermined margin. Introducing zero hydrocarbon air enables the evaporation monitoring to proceed without the necessity of altering the running count of hydrocarbons within the testing structure when such air is introduced to overcome the unacceptable pressure difference.  
         [0026]     As with prior approaches to evaporative emission monitoring, FID  116  is used to determine total hydrocarbon content of any given sample. An advantage of this invention is the addition of the gas analyzer  127  which is capable of determining up to six different specific types of hydrocarbons in the sample being emitted. This helps determine which vehicle systems are contributing to the evaporative emissions. For example, with the use of analyzer  127 , one can test a flexible fuel system, the refrigerant system of the vehicle, or even the tire inflation of the vehicle. The goal is to certify that the vehicle emissions are based only on the fueling system.  
         [0027]     Such isolation of emission problems to specific systems are speeded further by the optional probes  101  or  102  placed at specific locations on the vehicle. These probes were used in the prior art in a manner which caused delay time due to the long paths to the sampling equipment. With the use of a single heated sampling conduit  173  for both sampling of the interior ambient air of the testing structure as well as from probes  101  and  102  under the control of their respective control valves, the sampling time delays are considerably diminished.  
         [0028]      FIG. 2  sets forth a method  200  of conducting the evaporative testing with the apparatus described above in accordance with the principles of the invention. After starting the method at step  201 , pretest information is gathered as step  203 . Pre-test information may include, for example the test duration and the temperature profile to be used. Flame ionization detector  116  is then calibrated at step  205  in accordance with the known propane sources discussed previously. Next, at step  207  the test is initiated, wherein a vehicle under test is placed within the SHED interior and an initial air sample is taken to determine the hydrocarbon content and the component parts of such hydrocarbon content by units  116  and  127  of  FIG. 1 .  
         [0029]     The temperature inside the testing structure is then controlled at step  209  in accordance with a preselected temperature profile by equipment not shown.  
         [0030]     Pressure fluctuations within the testing structure which are initiated by temperature changes therewithin are controlled, and in accordance with periodic samples, the total grams of hydrocarbons exhaled due to the requirements of the pressure differential control are updated at step  211 .  
         [0031]     At step  213 , air samples are periodically taken via heated sample line  173  and the flame ionization detector  116  is also periodically calibrated. Gas analyzer  127  is calibrated offline, and its periodic calibration is not a part of the overall method set forth in  FIG. 2 .  
         [0032]     At step  215 , the hydrocarbon and/or component part data are collected for each sample, and a running count of the emissions is maintained by controller  180  of  FIG. 1 .  
         [0033]     At decision block  217 , if the duration period which is a predefined time period has not expired, the routine loops back to step  209  to repeat steps  211 - 215 . If the test duration has ended, an additional sample of the ambient air within the testing structure is taken to determine the final value of hydrocarbons and optionally the component parts thereof at step  219 . At step  221 , controller  180  determines the net grams of hydrocarbon that have been emitted by the vehicle during the test cycle, and the routine then ends at step  223 .  
         [0034]      FIG. 3  sets forth the method performed by controller  180  in monitoring the pressure differential between the outside atmosphere and the internal ambient air of the testing structure and for compensating the running total of emitted grams of hydrocarbons during the test interval.  
         [0035]     This method  300  begins at decision block  301 . If the pressure inside the testing structure is lower than the atmospheric pressure outside of the structure by a preselected tolerance, then the zero hydrocarbon air pathway of  FIG. 1  is opened at step  321 . If the pressure inside the testing structure is not below that of the outside atmosphere by a preselected tolerance, then the routine steps to decision block  303 . In decision block  303 , if the pressure of the ambient air within the testing structure is higher than the outside atmosphere by a preselected upper tolerance, then the SHED is allowed to exhale at step  307 . If the pressure differential for both upper and lower tolerances has not been exceeded, then the routine loops back to decision block  301 .  
         [0036]     If the pressure of the internal ambient air of the testing structure exceeds the outside atmosphere by the preselected tolerance level, then an exhale timer and counter is initiated at step  305 , the SHED outlet exhale port of  FIG. 1  is opened at step  307  and simultaneously the exhale pump is turned on at step  309 .  
         [0037]     If the testing structure has zero hydrocarbon air injected at step  321  or if the exhale initiation steps of  305 ,  307  and  309  are initiated, then the routine enters decision block  311 . Again, the pressure differential between the inside and outside of the testing structure is monitored and if it is within a tolerance level, the routine proceeds to decision block  313 . If the pressure differential is not within tolerance, then controller  180  of  FIG. 1  increments a counter for accumulating the total hydrocarbons being emitted within the testing structure, and the volume of emitted air is accumulated corrected to standard temperature and pressure (STP).  
         [0038]     At decision block  313 , controller  180  determines if the testing structure was inhaling (i.e. being injected with zero hydrocarbon air). If the testing structure was inhaling, then the zero air supply solenoid control valve is closed at step  325  and the routine returns to decision block  301 .  
         [0039]     If the testing structure was not inhaling at step  313 , then it must have been exhaling. The SHED opening for exhaling is closed at step  315  and simultaneously at step  317  the amount of exhaled grams of hydrocarbons is calculated in accordance with the monitored flow rate and saved. At step  319 , the exhaled hydrocarbon grams are added to the emission running count, and the routine returns to step  301 .  
         [0040]     In this manner, a running count of emitted hydrocarbons (and their constituent components) is maintained via periodic sampling through conduit  173  and, if the interior of the testing structure exhaled air to overcome pressure differentials, this running count is compensated by adding hydrocarbons which were bled off from the testing structure during the routine. By using substantially zero hydrocarbon containing air as an injector into the testing structure to raise the pressure therein, no compensation is required.  
         [0041]     The invention has been described with reference to a preferred embodiment, for the sake of example. The scope and spirit of the invention are to be determined by appropriately interpreting the appended claims.