Land vehicles: bodies and tops – Tops – Roof structure
Reexamination Certificate
1999-11-02
2001-06-12
Pedder, Dennis H. (Department: 3612)
Land vehicles: bodies and tops
Tops
Roof structure
Reexamination Certificate
active
06244654
ABSTRACT:
The invention relates to a sliding roof for motor vehicles, with which the resonance noise, the so-called sliding roof buffeting noise, which occurs frequently in motor vehicles with an open sliding roof, can be reduced significantly or even eliminated completely.
In the event that the sliding roof is open, an unpleasant, low frequency resonance of the interior of the vehicle can occur at low speeds of, for example, 50 km/h. This is referred to as sliding roof buffeting noise or simply as buffeting noise and is encountered primarily in the case of large capacity limousines and station wagons. The buffeting noise increases as the size of the sliding roof increases, as it does evermore in modern vehicles.
Some concepts relating to sliding roofs are defined in the following to clarify the rest of the specification. The sliding roof cutout is the cutout in the sliding roof in the outer sheet metal of the roof of the vehicle. The sliding roof opening is the opening to the interior of the vehicle, which is defined by the configuration of the upper boundary of the vehicle interior. A sliding cover, movably mounted, serves to open and close the sliding roof. Depending on the actual position of the sliding cover, the latter covers a portion of the sliding roof opening, so that there is a clear opening to the interior of the vehicle, which is referred to in the following as the resulting clear sliding roof opening. The distance between the, as seen in the driving direction, front edge of the resulting clear sliding roof opening and the rear edge of the latter is the opening length of the resulting clear sliding roof opening.
Physically, the occurrence of the buffeting noise can be explained by the principle of exciter and resonance body. The role of exciter is assumed by the shear layer over the resulting clear sliding roof opening, which arises due to the collision between the air flowing along the outside of the vehicle and the air in the interior of the vehicle. The interior of the motor vehicle assumes the function of the resonance body. When the sliding roof is open, this motor vehicle interior can be regarded as a Helmholtz resonator; that is, the resonance frequency of the interior depends on the size of the resulting clear sliding roof opening and on the volume of the interior of the vehicle.
The excitation of the interior to resonance can be explained as a consequence of the instability of the shear layer. The smallest obstructions in the front region of the sliding roof are already sufficient to excite the shear layer to oscillate. These oscillations are stimulated downstream. The flow, so disturbed, strikes the rear edge of the resulting clear opening of the sliding roof. Periodically alternatively, it is flushed over this edge and pressed into the interior of the vehicle, the latter causing a pressure wave. A portion of this pressure wave moves upstream and, in a fixed phase relationship to the preceding disturbance, leads there to a fisher stimulation of the shear layer. A self-reinforcing shear layer oscillation, with a dominating main frequency, which is shifted to higher frequencies as the speed of the vehicle increases and depends on the opening length of the resulting clear sliding roof opening, arises in this manner. If this excitation frequency is identical with the resonance frequency of the interior and if the amplitude of the oscillations, in what is the rear region in the driving direction, of the resulting clear sliding roof opening, is sufficiently large, then is perceived as a sliding roof buffeting noise.
It is an object of the invention to provide a sliding roof, which can interfere selectively with the aerodynamic excitation mechanism of the buffeting noise. The buffeting noise shall be reduced to a level, which can no longer be perceived subjectively.
This objective is accomplished by the object of claim
1
. Advantageous developments of the invention are the objective of further claims.
The inventive device involves a modification of the geometry of the corners of the sliding roofs with an essentially rectangular or trapezoidal, resulting, clear sliding roof opening by the complete or partial covering of at least one of the rear corner regions, as seen in the driving direction, of the resulting clear sliding roof opening. This inventive modification can be realized, for example, in the following way:
By a further development of sliding roofs with essentially rectangular, but also trapezoidal, resulting sliding roof openings, for example, by providing a folding, sliding, turning or stretching mechanism for extending or stretching different embodiments of the inventive covering in the event that the opening lengths of the resulting clear sliding roof opening are critical with respect to buffeting noise or by a corresponding retrofitting of existing sliding roofs with an essentially rectangular or trapezoidal resulting clear sliding roof opening.
New sliding roofs, which are to be developed, alternatively can receive a resulting clear sliding roof opening which, starting out from an essentially rectangular resulting clear sliding roof opening, receives a shape corresponding to the above-mentioned corner covering.
A combination of a partial shape change of an original essentially rectangular resulting clear sliding roof opening and partially of a covering, which can be added on, is also conceivable.
The fluctuations of the shear layer flow and the sliding roof opening, as an exciter of the resonance, increase from the middle of the vehicle to the outside. Since the disturbances in the shear layer, as described above, also increase in the direction of flow, the fluctuations are greatest in the rear outer region of the rectangular or trapezoidal resulting clear sliding roof opening. With the inventive device, the outer fluctuations, which are the main cause of the excitation of the interior, are selectively repressed or disturbed, so that the resonance oscillations can no longer be perceived as a buffeting noise.
The inventive device enables the opening length of the resulting clear sliding roof opening to be enlarged more than previously without having a buffeting noise arise. At higher driving speeds, there are no additional flow noises caused by the device.
After adaptation to the respective physical and geometric factors, the effectiveness of the inventive device can be demonstrated in wind tunnel and driving experiments on any vehicles generating the buffeting noise in their basic configuration. This proof can be furnished by subjective perception as well as by measurement.
The advantages, associated with the invention, can be seen to be therein that the buffeting noise cannot be reduced in such a manner with any other known measures of comparable low expense for comparable opening lengths of the resulting clear sliding roof opening without the generation of additional, extremely undesirable noises. Admittedly, an appreciable lowering in the buffeting noise level is possible with wind deflectors or other flow deflectors mounted in the region of what, in the driving direction, is the front edge of the sliding roof cutout. However, flow noises, that is, wind rushing noises or whistling, generated by these devices, occur at higher speeds. A complete elimination of the buffeting noise can at times not be achieved for certain types of vehicles by means of wind deflectors having dimensions acceptable by customers. A reduction in the buffeting noise by means of an only partially open sliding cover and, with that, a smaller, resulting, clear sliding roof opening at driving speeds, which tend to form buffeting noise, is also not desirable because of the appreciable blocking of vision. For the proposed device, the blocking of vision is reduced to a tolerable extent and the opening length of the resulting clear sliding roof opening even remains unchanged in the middle region. Additional wind rushing noise or whistling at higher speeds has not been noted.
Possible areas of application of the invention, aside from reducing the buffeting noise of sliding roofs, arise f
Borchers Ingo
Borgwardt Ralph
Braehler Boris
Laemmlein Stephan
Daimler-Chrysler AG
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Pedder Dennis H.
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