Figure 18.5 One of the levelled steel plates exactly levelled and cast in the pit floor to support the chassis dynamometer (one per dynamometer HD bolt location)
The need to run subfloor cable and ventilation ducts, between the control room and the pit and the drive cabinets and the pit requires preplanning and collaboration between the project engineer and builder, it can also complicate the task of creating a watertight seal against ground water. Normally there will be the following subfloor ducts:
signal and separate small power cable ducts between control room and dynamome- ter pit;
high power drive cables and separate signal cable ducts between the drive cabinet room/space and the dynamometer pit;
pit ventilation ducts which at a minimum will have to include a purge duct for removal of hydrocarbon vapours (see ATEX requirements, Chapter 4).
On the wall of the test cell it is usual to fit a ‘break-out’ box that allows transducers, microphones or CAN bus plugs to be used for special vehicle-related communications between control room and test unit.
Project managers of any major test facility building are advised to check the layout and take photographic records of all substructure service pipes and steel work before concrete is poured.∗∗
When, due to diminishing access, the dynamometer has had to be located in its pit before the building has been completed and before permanent electrical services are available, it may be vulnerable until building completion to the pit flooding and roll surface damage; provision must be made to guard against both eventualities.
Pit flooring
In most large chassis dynamometer projects, the false floor and its support structure are provided by the dynamometer manufacturer. It may be centrally supported by the dynamometer structure and will have access hatches for maintenance and calibration equipment. The steel or aluminium floor plates will be lifted from time to time and any hatches will need to be interlocked with the control system. It will be clear to readers that unless the pit shape is built to a quite precise shape and size, there will be considerable difficulty in cutting floor plates to suit the interface and that errors in this alignment will be highly visible. It is strongly recommended that the civil contractor should be supplied with the pit edging material by the chassis dynamometer manufacturer and that it is cast into the pit walls under his supervision before final edge grouting. In some cases the pit edging assembly can be fixed with jig beams in temporary place to hold the rectangular shape true while fixing (Fig. 18.6).
∗∗ AJM was once told by a steel fixer that his trade was comparable with that of a surgeon in that they both bury their mistakes; henceforth detailed records have been made of prepour structures.