Brakes – Operators – Electric and mechanical
Reexamination Certificate
1999-09-30
2001-04-03
Graham, Matthew C. (Department: 3613)
Brakes
Operators
Electric and mechanical
C188S164000, C188S158000, C188S267000
Reexamination Certificate
active
06209688
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an eddy currect reduction brake apparatus for large sized vehicles or the like, and, more particularly, to an eddy current reduction brake apparatus in which magnetic flux of a permanent magnet is effectively applied to a brake drum.
In conventional eddy current reduction braking systems, ferromagnetic plates have substantially rectangular cross sections and outer and inner surfaces of substantially the same area. Consequently, magnetic flux from the magnets is not concentrated by the ferromagnetic plates onto a brake drum. If the ferromagnetic plates are shaped as trapezoids, and the area of outer surfaces made narrower than the areas of inner surfaces, it is possible to concentrate the magnetic flux entering the brake drum and thereby increase magnetic flux density and enhance brake force. However, in the aforementioned construction, the edge effect concentration of magnetic flux is difficult to obtain, and it is difficult to cast the ferromagnetic plates into an outer tubular portion of a guide tube made of aluminum. Furthermore, even if the guide tube is manufactured by forging, allowance for machining of the outer and inner peripheral surfaces of the outer tubular portion increases and the volume of the ferromagnetic plates decreases because of a resultant parting line. In eddy current reduction braking systems having an immovable magnet support tube and a movable magnet support tube axially arranged in a hollow portion of a guide tube, a non-braking condition produces on the brake drum a dragging torque. Therefore, it is necessary to thicken the ferromagnetic plates and increase the volume in order to suppress the dragging torque, which is dis-advantageous in terms of braking performance.
In eddy current reduction braking systems in which a good conductor such as copper is coated or deposited on the opposite ends of a brake drum, brake force can be enhanced by ferromagnetic plates of rectangular shape and without roundness at corner portions. However, the entire periphery of the sides of the ferromagnetic plates have to be machined and a parting line eliminated by machining. Thus, even if the ferromagnetic plates are cast into a guide tube made of aluminum, the ferromagnetic plates are attracted by the brake drum such that the ferromagnetic plates can possibly move out of the guide tube. Furthermore, the guide tube contracts substantially during a cooling period after ferromagnetic plates have been cast, and cracks possibly occur in portions adjacent to corner portions of the ferromagnetic plates in the guide tube.
In the conventional eddy current reduction braking systems disclosed in Japanese Patent Laid-Open Nos. 6-38504 and 6-38505 publications or the like, side sections of ferromagnetic plates are shaped such that an outer surface of a rear portion protrudes rearwardly in a rotational direction of a brake drum, and a rear surface is inclined in a direction opposite to the rotational direction of the brake drum. The above-described construction is intended to disperse magnetic flux from the magnets to the brake drum to enhance the braking performance. However, it has been found that at the high speed rotation of the brake drum, the magnetic flux exerted on the brake drum is concentrated, rather than being dispersed, so as to enhance the edge effect of the ferromagnetic plates, and contribute to an increase in braking force.
SUMMARY OF THE INVENTION
The present invention is an eddy current reduction braking system in which with high speed rotation of a brake drum, magnetic flux produced by magnets is concentrated to increase magnetic flux density and thereby enhance braking force. According to the invention, there is provided a guide tube formed of a non-magnetic material and having a hollow portion in the shape of a rectangle in section disposed interiorly of a brake drum. A number of ferromagnetic pole pieces are disposed at annularly equal intervals on an outer surface of the guide tube and at least one magnet support tube is movably mounted in the hollow portion of the guide tube. Magnets are mounted on the magnet support tube such that their polarities with respect to the ferromagnetic pole pieces are alternately different. In addition, each pole piece has an outer surface of area less than that of an inner surface thereof, and the inner surface includes a portion circumferentially displaced from the outer pole piece surface in a direction opposite to a given direction of brake drum rotation.
Preferably, a side section of each ferromagnetic pole piece is made similar to a parallelogram. This provides a desired flux concentration edge effect in a front portion facing the rotational direction of a brake drum without a requirement for excessive machining of the ferromagnetic pole pieces prior to casting. Because of the shape of the pole pieces, magnetic flux reaching the brake drum from the magnets is concentrated at the front end portions in the given direction of brake drum rotation. Preferably, the front surface of each ferromagnetic pole piece is inclined in the given rotational direction from the inner surface toward the outer surface of the pole piece, and the thickness of the rear half portion of each ferromagnetic pole pieces is gradually reduced in a direction opposite to the given rotational direction. For example, the rear surface of each ferromagnetic pole piece can be inclined from the inner pole piece surface toward the outer pole piece surface. However, when the thickness of the rear portion of the ferromagnetic pole piece is too thin, the passing of magnetic flux is weakened, and the magnetic flux leaks outside when in a non-braking condition. It is therefore preferable that the thickness of the rear portion of the ferromagnetic plates is made thinner stepwise or in a stepwise manner to prevent a leakage of magnetic flux when in the non-braking condition.
REFERENCES:
patent: 2525571 (1950-10-01), Winther
patent: 3488535 (1970-01-01), Baermann
patent: 3601641 (1971-08-01), Baermann
patent: 4146805 (1979-03-01), Fehr et al.
patent: 4937483 (1990-06-01), Matsui et al.
patent: 5054587 (1991-10-01), Matsui et al.
patent: 5303802 (1994-04-01), Kuwahara
patent: 5337862 (1994-08-01), Kuwahara
patent: 6041897 (2000-03-01), Saumweber et al.
patent: 6-38504 (1994-02-01), None
patent: 6-38505 (1994-02-01), None
Graham Matthew C.
Isuzu Motors Limited
Jarcho Harold G.
Pezzlo Benjamin A
Toupal John E.
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