Ruído, vibração e aspereza

501-25-90 Body Repairs - General Information 501-25-90 DESCRIPTION AND OPERATION Noise, Vibration and Harshness Noise, coming from the vehicle and which can be heard inside and outside the vehicle. Vibrations, oscillations that are felt and noticeable inside the vehicle. Harshness, noises which come from the vehicle and which can be heard, felt and noticed inside and outside the vehicle. These terms are grouped together under the title Noise, Vibration, Harshness, or NVH for short. The task of vehicle development and production is to ensure that noises caused by the vehicle do not disturb the driver and passengers. Moreover, the the external noises emitted by the vehicle must not exceed the thresholds set by law. NOTE: Basic and advanced training courses are offered for the following contents. For an overview of all courses offered, please refer to the Ford Service Organisation's training course brochure. Noise types and causes Noises in and around the vehicle are assigned specific descriptions: ‡ Humming and droning are perceived as low tones. ‡ Buzzing and whirring are middle tones. ‡ Howling, whistling, squeaking are assigned to the high tones. Low to middle tones are considered to be unpleasant. They are palpable and noticeable as oscillations and vibrations throughout the body. Loud howling and whistling is painful to the ears. A noise usually consists of a superimposition of different tones which spread as oscillations. Each of these oscillations has a specific oscillating time and can be measured in frequencies. The frequency describes the number of oscillations per second. The frequency unit is specified in Hertz (Hz). The human ear can perceive frequencies between 20 and 20000 Hz. Where the different notes come from in a vehicle: ‡ Low notes are mostly produced by the engine. ‡ Low tones can also be produced by the roadbed, particularly on rough surfaces. This is a form of droning which can be felt by the vehicle occupants as vibration or roughness. ‡ High tones however, which are experienced as howling or whistling noises, are often air currents (wind noises) or come from ancillary components such as the generator, power steering pump or drivebelt. ‡ There are also clattering noises which can occur when driving over an uneven road. These jerking noises are produced by, for example, the shock absorbers, chassis components or loose articles inside the vehicle. Noises can already be contained where they occur or, if this is not possible, can be confined with suitable measures. The basic procedures here are the damping of oscillating parts, the insulation of components or the absorption of the noises through appropriate materials. Damping If a damper is installed next to an oscillating mass, the characteristic of the damper will reduce the movement of this mass accordingly (e.g. bumper on chassis). Damping affects the resonance of an object or system. Isolation In oscillation technology, the term isolation means decoupling (separation) of components and systems. An engine is mounted in sprung elements, so that as little oscillation as possible is passed to the vehicle. In automotive technology, the isolation technique used is nearly always rubber mounting. Rubber has a large internal damping capacity. The elasticity of the rubber acts like a spring. Absorption Sound waves are reflected from hard surfaces Through the use of absorption material, sound waves hit soft surfaces and are absorbed by them. The composition and thickness of the material used plays an important role here. A soft surface, depending on its composition, absorbs the sound waves and reduces their energy. NVH elements NVH elements are installed to prevent airborne sound transfers to the passenger compartment in different body cavities.