Disc brake

Details Disc brake Disc brake

1999-03-19

2001-02-13

Butler, Douglas C. (Department: 3613)

Brakes

Wheel

Axially movable brake element or housing therefor

C188S20500R, C188S073350

Reexamination Certificate

active

06186289

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to disc brakes for use on automotive vehicles.
A known disc brake for a motor vehicle typically includes a pair of in board and outboard brake shoes or pad assemblies placed on opposite sides of a rotor rotatable with a wheel to be braked and slideably supported on a carrier secured to a non-rotatable part of the vehicle. When a brake pedal is depressed, a caliper is moved on the carrier to urge the in board and outboard pad assemblies into frictional engagement with opposite sides of the rotor so as to apply the necessary clamping force thereto.
A problem associated with such a conventional disc brake is the frequent occurrence of a low frequency noise or squeal when the pad assemblies are pressed against the rotor. Such a noise is obviously uncomfortable to the driver. There is thus a need to substantially reduce the number of occurrences of such a low frequency noise.
An attempt has been made to reinforce the most deformed part of a carrier to increase its rigidity, as disclosed in Japanese laid-open patent publication No. 7-259901. This attempt is effective in reducing the extent of vibrations, but fails to reduce the number of occurrences of a low frequency noise (see FIG.
7
).
Through an extensive search, the inventor has found that the occurrence of a low frequency noise of, for example, 1.8 kHz, is more closely related to vibrations of a carrier than to any other part of a disc brake. The carrier has various modes of vibration such as bending and torsion modes of vibration. The carrier typically includes a pair of inner arms located on the in board side of a rotor and having a pair of guides along which an in board brake pad assembly is axially moved, a pair of outer arms located on the outboard side of the rotor and having a pair of guides through which an outboard brake pad assembly is axially moved, an inner beam extending between the two inner arms and secured to a knuckle or other fixed part of a vehicle, and an outer beam extending between the two outer arms. In the torsion mode, the inner arms are twisted in opposite directions. This is also the case with the outer arms. In the bending mode, the inner and outer arms are bent about an axis parallel to the axis of the rotor. It has been found that these two different modes of vibration interact to cause a self-exited vibration and thus, a low frequency squeal.
In the disc brake shown in Japanese laid-open patent publication No. 7-259901, the difference in natural frequency between the bending and torsion modes is even less than that of the typical carrier known in the art (see FIG.
7
). It is believed that an increase in rigidity of the carrier does not bring about a reduction in the number of occurrences of the low frequency noise.
Accordingly, it is an object of the present invention to provide a disc brake which enables a substantial reduction in the number of occurrences of a low frequency noise or squeal without the need for additional parts and without increasing its production cost and weight.
SUMMARY OF THE INVENTION
To achieve the foregoing object, the present invention provides an improved disc brake comprising a carrier adapted to be secured to a fixed part of a vehicle, such as a knuckle, a pair of in board and outboard pad assemblies located on opposite sides of a disc or rotor rotatable with a wheel to be braked, and a caliper extending over the periphery of the rotor and axially moved to urge the in board and outboard pad assemblies into frictional engagement with opposite sides of the rotor. As a feature, the carrier is constructed such that the difference between the natural frequency in a bending mode and that in a torsion mode is at least 300 Hz. This large difference in natural frequency between the two modes of vibration can avoid undesirable interaction therebetween and thus, eliminate the occurrence of a low frequency noise.
In a preferred embodiment, the carrier includes an inner beam secured to the fixed part of the vehicle and an outer beam connected to the inner beam in an axially spaced relation. The inner beam has a moment of inertia of area when bent and a polar moment of inertia of area when twisted. The inner beam has a moment of inertia of area/polar moment of inertia of area ratio of at least 0.75. In this design, the inner beam is twisted as much as a typical inner beam known in the art, but better resists bending stress. In other words, the carrier has a higher natural frequency in the bending mode than in the torsion mode.
In one embodiment, the inner beam has a pair of upper flanges, a pair of lower flanges and a pair of intermediate flanges connected to the upper and lower flanges by respective ribs. Alternatively, the inner beam may have a gourd-shaped section. Still alternatively, the inner beam may have a T-shaped, inverted T-shaped, C-shaped or inverted C-shaped section.


REFERENCES:
patent: 4047598 (1977-09-01), Thrower
patent: 5564532 (1996-10-01), Baba et al.
patent: 5566791 (1996-10-01), Ohishi
patent: 7-259901 (1995-10-01), None

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