Figure 18.4 A single roll set (2×2) chassis dynamometer plus road speed following cooling fan, within a cell sized to test rear and front wheel drive cars (AVL Zöllner)
The dynamometer pit can be kept at a constant temperature above or below that of the chamber by passing treated (factory) air through the pit via ducts cast in the floor (see Fig. 18.4). This strategy submits portions of the roll’s surface to differential temperatures during the static cooldown phase but without reported problems.
The pit can be allowed to chill down to the cell temperature but the parts of the chassis dynamometer that are crucial to accurate and consistent performance, such as bearings and load cell, are trace heated.
Whatever the layout components exposed to temperatures below 25?C such as rolls and shaft should be constructed of steel having adequate low-temperature strength to avoid the risk of brittle fracture.