| Popis: |
Retrofit noise control techniques were developed to reduce noise exposure for the operator of a large Army forklift truck. The Army's Rough Terrain Forklift Truck (RTFT) is a large load-handling and towing vehicle weighing over 34,000 lbs., with selectable two-wheel or four-wheel drive and steering. Power is provided by a rear-mounted two-cycle V-6 engine with a Roots type blower. Vehicle power steering, power braking, and material handling functions are accomplished by a complex hydraulic system. In the comprehensive noise reduction program, various noise sources were studied and modified. Both moving and stationary tests were conducted, and major vehicle noise sources were characterized. Pulsation damping devices and the replacement of hydraulic pumps were studied. The impact of hydraulic system modifications on vibration levels was assessed, as well as final operator position noise levels without cab. Conventional noise analysis techniques, such as spectral analysis of sound and vibration signals, selective or isolated operation of different noise sources, and the window technique, were used to separate the contribution of hydraulic noise from that of other noise sources, and to define the nature of the hydraulic noise problem. It was found that hydraulic system noise was more difficult to reduce, at least on a retrofit basis, than other common vehicle noise sources. Practical retrofit modifications to reduce hydraulic system noise included component replacement, introduction of flexible fluid lines, vibration isolation, and vibration damping. Overall noise at the operator's ear was reduced by 15 dB(A) without a cab and by 22 dB(A) with a cab. |
