Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:9:p21
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 9 (pt 21/37)
Character Range: 1837073–1840260

be calibrated before its initial use and at appropriate service intervals thereafter. An appropriate service interval shall be either equipment manufacturer recommendation or according to good engineering practice.

              4.1. Chassis dynamometer

               The chassis dynamometer shall meet the requirements of paragraphs 2. to 2.4.2. inclusive of Annex B5.
              4.2. Evaporative emission measurement enclosure
               The evaporative emission measurement enclosure shall be a gas-tight rectangular measuring chamber able to contain the vehicle under test. The vehicle shall be accessible from all sides and the enclosure when sealed shall be gas-tight in accordance with paragraph 4.2.3.3. of this annex. The inner surface of the enclosure shall be impermeable and non-reactive to hydrocarbons. The temperature conditioning system shall be capable of controlling the internal enclosure air temperature to follow the prescribed temperature versus time profile throughout the test, and an average tolerance of 1 °C over the duration of the test.
              The control system shall be tuned to provide a smooth temperature pattern that has a minimum of overshoot, hunting, and instability about the desired long-term ambient temperature profile. Interior surface temperatures shall not be less than 5 °C nor more than 55 °C at any time during the diurnal emission test.
              Wall design shall be such as to promote good dissipation of heat. Interior surface temperatures shall not be below 20 °C, nor above 52 °C for the duration of the hot soak rest.
              To accommodate the volume changes due to enclosure temperature changes, either a variable-volume or fixed-volume enclosure may be used.
              4.2.1. Variable-volume enclosure
               The variable-volume enclosure expands and contracts in response to the temperature change of the air mass in the enclosure. Two potential means of accommodating the internal volume changes are movable panel(s), or a bellows design, in which an impermeable bag or bags inside the enclosure expand(s) and contracts(s) in response to internal pressure changes by exchanging air from outside the enclosure. Any design for volume accommodation shall maintain the integrity of the enclosure as specified in paragraph 4.2.3. of this annex over the specified temperature range.
               Any method of volume accommodation shall limit the differential between the enclosure internal pressure and the barometric pressure to a maximum value of 0.5 kPa.
               The enclosure shall be capable of latching to a fixed volume. A variable volume enclosure shall be capable of accommodating a +7 per cent change from its "nominal volume" (see paragraph 4.2.3.1.1. of this annex), taking into account temperature and barometric pressure variation during testing.
              4.2.2. Fixed-volume enclosure
               The fixed-volume enclosure shall be constructed with rigid panels that maintain a fixed enclosure volume, and meet the requirements below.
              4.2.2.1. The enclosure shall be equipped with an outlet flow stream that withdraws air at a low, constant rate