The present invention relates to a device for reducing certain sound ranges of tire/road noise emitted by a motorized vehicle, whereby in the area of sound projection of the tire/road surface noise sound absorbers in the form of resonators are arranged that are adjustable to sound ranges the frequencies of which change proportional to the rpm of the wheel. Two of three alternatives of the invention require the presence of ABS (anti-lock braking system).
The noise caused by traffic is one of the most disturbing sources of noise pollution. The noise sources of a motorized vehicle are engine and tires whereby on high-speed thoroughfares and cobblestone surfaces, especially when the surfaces are wet, the tire/road surface noise is predominant. Since the increased use of sound proofing encapsulations for the engine, the tire/road surface noise has become more prominent. Truck tires, due to their construction, cause a more unpleasant rolling noise than automobile tires. From the standpoint of financial and aesthetic reasons, measures that can be undertaken directly at the source of noise are especially advantageous.
For automobile and truck tires it has been conventional for the last couple of years to provide the tread elements or blocks arranged sequentially in the circumferential direction of the tire with different circumferential lengths (pitch). For example, it is conventional to select three to five different pitch lengths with suitable length ratios relative to one another and with a favorable arrangement (pitch sequence) over the circumference of the tire while taking into consideration other tread properties.
The object is in general the randomization of the tire/road surface noise, which results especially in a distribution of the occurring frequencies over a broader frequency band.
However, it still cannot be prevented that the tire at certain frequencies, which change proportional to the rpm of the wheel, emits sound pressure. These frequencies can be detected as a permanent peak in a so-called order spectrum. These peaks may have different causes, for example, the mold partition of the vulcanization mold, the total number of pitches over the circumference of the tire, the actual geometry of the pitches (tread blocks) or possible periodic occurrences within the pitch sequence. For example, it is known to a person skilled in the art that a tire with, for example, 70 pitches (tread elements) over the circumference of the tire emits dominantly the 70th harmonic of the rpm of the wheel, which however is not always true because the different causes overlap one another and have an effect on one another. In general, it can be said that the rolling noise of each tire comprises sound ranges with discrete frequencies or a narrow frequency band at which predominant sound pressure can be detected the frequencies of which change proportional to the number of revolutions (rpm) of the wheel.
From German Patent 34 28 468 a device is known that is mounted to the vehicle wheel and rotates with the wheel. The device comprises one or more resonators with hollow chambers the volumes of which are controlled as a function of the velocity by centrifugal forces. The resonators may be partly embodied as Helmholtz resonators.
From German Offenlegungsschrift 37 29 765 a device is known that is arranged in the area between the rear partition of the passenger compartment and the trunk and which comprises an arrangement of Helmholtz resonators of a large volume. This device is designed to combat especially sound ranges below 80 hertz.
It is therefore an object of the present invention to provide a device for reducing tire/road surface noise, especially such sound ranges that change their frequency proportional to the speed of the motorized vehicle.