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 Hydrocarbon content of any withdrawn ambient air is determined from the latest sample, and cumulative evaporative emissions are adjusted accordingly.

Abstract: A method and apparatus calibrates an exhaust gas measurement system for a motor vehicle. The method includes the steps of providing a flow of air to the exhaust gas measurement system having a known flow rate, measuring and storing a signal output from the exhaust gas measurement system, repeating the first two steps a predetermined plurality number of times, calculating a calibration curve based on the known flow rates and the stored signal; and using the calibration curve in the exhaust gas measurement system.

Abstract: A computer controlled sealed housing evaporative determination (SHED) testing apparatus and method are provided for testing evaporative emissions for a motor vehicle. The SHED testing apparatus includes a substantially air-type testing structure for enclosing a subject motor vehicle and containing a quantity of ambient air. The ambient air is sampled at the beginning and end of a given test to measure the amount of hydrocarbons present therein. The apparatus undergoes a predefined testing procedure in which temperature of the air within the sealed testing structure is controlled in a predefined manner. To account for pressure changes due to the changing temperature, a portion of the ambient air contained within the testing structure may be evacuated from or introduced into the testing structure so as to maintain a substantially constant pressure differential of zero.