Chassis dynamometer pit design and construction details
The minimum requirements, if not the exact specification, of the pit into which a chassis dynamometer is to be installed will invariably be provided by the dynamome- ter’s manufacturer which will include the loading on the pit floor to aid the structural designer. The pit must be built to a standard of accuracy rather higher than is usual in some civil engineering practice since all pit installed dynamometers have a close dimensional relationship with the building in which they are installed; this is par- ticularly true for the pit construction which has to meet three critical dimensional standards:
1. The depth of the pit in relation to the finished floor level of the test cell needs to be held to tight dimensional and level limits. Too deep is recoverable, too shallow can be disastrous.
2. 3.
Engine Testing
The lip of the pit has to be finished with edging steel that interfaces accurately with the flooring plates that span the gap between the exposed rolls’ surface and the building floor. The centre line of the dynamometer has to be positioned and aligned with the building datum and the vehicle hold-down structure that may also be cast into the cell floor. Fine alignment can be achieved by the dynamometer installers, but movement at that stage will be very restricted.
Pit depth
To achieve point 1 above, it is normal practice to make the pit floor lower than the datum dimension and then cast into the floor levelled steel ‘sole plates’ at the required height minus 5–10 mm to allow some upward adjustment of the machine to the exact floor level. The final levelling can be done by some form of millwright’s levelling pads, or more usually levelling screws and shim plates, as shown in Fig. 18.5.
The system described above allows the pit floor to have some slight ‘fall’ towards a small drainage sump fitted with a level alarm or float operated pump. If the site has a high water table, the pit will have been suitably ‘tanked’ before final concrete casting to prevent ground water seepage; however, spillage of vehicle liquids and cell washing will drain into the pit so a means of taking these liquids into a foul liquid intercept drain is advisable.