The interior dimensions of the measurement facility are approx. lenght x width x height = 25 x 18,9 x 6 cbm, access is provided by a gate with an opening of approx. 3 x 3 m2 for light trucks. An additional door connects the measurement facility and the adjacent control room. The ceiling, walls, doors and gates are lined with absorbers developed by the Fraunhofer IBP, the asymmetrically structured absorber and broadband compact absorber, in such a way that a semi-anechoic field with 40 Hz lower cut-off frequency is present in the measurement facility. The background noise level for the measurement facility amounted to 25 dB(A), at maximum room ventilation to 30 dB(A) and with additional maximum vehicle cooling system to 55 dB(A). The floor is hard-walled and equipped with a plastic coating. The ventilation systems supplies adjustable air flows of up to 40.000 cbm per hour. The routing of the air is effected by slots in the frontal wall and ceiling edges. HVAC allows conditions of 23°C ± 5°C at full-load operation and normal outdoor temperatures from -10°C to 30°C. On each of the two long walls 30 microphones are installed at a distance of 7.5 m to the test bench center for the measurement of simulated pass-by noise. Openings in the floor are installed in the center of the microphone paths and close to the vehicle for housing the front-ends of the acoustic data acquisition system. The floor has cut-outs at the microphone paths to accommodate microphone cables.
Roller Test Bench
The testing technology consists of a 4-wheel roller test bench with individually driven rollers having a diameter of 75 inches and a perimeter of 6 m. The roller width is 550 mm and the exterior wheel track 2200 mm. The rear pair of rollers is infinitely variable for a wheel base from 2200 mm to 4000 mm with a positioning precision of ± 1 mm. All rollers can be adjusted to a common zero point. The test facility is suited for vehicles of a total weight from 800 kg to 4000 kg at a maximum axle weight of 2500 kg. The vehicles can be tied up by ropes, rods or at the wheel hubs.
With an input power of 300 kW per roller the test facility is suitable for a drive speed of up to 320 kg/h and provides a constant tensile force of 7500 N up to 120 kg/h so that an acceleration of almost 1 g is achieved. High-precision control guarantees an exact synchronization of the rollers. Load cycle change tests, where electronic automotive safety systems like ABS and ESP can have an influence on the test bench control system, require a maximum deviation of the speeds between the rollers of the front and rear axles of 0.5 km/h at maximum acceleration and of 0.2 km/h at moderate accelerations or constant speeds. This is to ensure that these auxiliary programs are not activated. For low-speed tests with bars mounted on the rollers of one axle the deviation must not exeed 1 mm to avoid double pulses.
Parameters controllable from the control room and partly from the vehicle by means of a remote control comprise distance, speed, acceleration, tensile force, mass simulation and driving resistance simulation. The variables are individually controllable at all four rollers.
A pallet system, which totally replaces the test facility cover, is used for an efficient workflow in the test facility and thus rapid and reproducible exchange of vehicles. The vehicle is fixed on the pallet, prepared and moved to the test facility by means of air cushions. The pallet is set in there and fixed instead of the cover. Two different types are used: One pallet for exterior noise measurements with roller openings and otherwise completely closed surface with reverberant coating as well as pallets for vehicle investigations of all kinds with groove rails and an opening for the pit. The pallet for exterior noise measurements is lifted to the ceiling of the measurement facility for storage by motorized devices. In the process, the absorber lining is opened and closed afterwards by motorized wings. The other pallets can be moved with the vehicle to the preparation rooms and be stored there.