Brakes – Operators – Electric
Patent
1991-10-11
1996-01-23
Graham, Matthew C.
Brakes
Operators
Electric
188156, H02P 1500
Patent
active
054859018
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an electromagnetic brake, and particularly to a brake having a function of rotating a rotor made of a conductive material in a magnetic field to thereby cause an eddy current in the rotor, the eddy current converting the rotational energy into heat to produce a braking torque, and the converted heat being radiated.
DESCRIPTIONS OF RELATED ART
As engine functions and expressways are improved, large- and middle-sized trucks frequently run at high speeds for long distances, and to reduce a load on a main brake, the braking torque of which is controlled by a liquid pressure, an auxiliary brake such as an electromagnetic brake is employed.
The electromagnetic brake must not cause a driver discomfort when changing the braking torque in a stepwise manner by changing the number of energized electromagnetic coils, but must provide smooth braking characteristics by controlling the current flowing to the electromagnetic coils.
According to a conventional electromagnetic brake, the temperature of a rotor can become higher than 600.degree. C., depending on operating conditions such as an inclination of a road, an operating time, and the load, and this high temperature has an adverse affect on the periphery of, and thus deforms, the rotor.
To solve this problem, there must be provided a brake that achieves smooth braking characteristics by controlling the temperature of a rotor and current flowing to electromagnetic coils, and prevents an excessive increase of the temperature of the rotor.
FIG. 1 is a schematic view showing a conventional electromagnetic brake.
In FIG. 1, the electromagnetic brake used for a large- or middle-sized vehicle comprises, for example, eight electromagnetic coils (L1 to L8) 2 disposed on the stationary side of a transmission of an engine 1, a rotary drum 3 disposed on a propeller shaft 3a for transmitting a torque to wheels 6, a relay circuit 4 including relays RL1 to RL8 connected to the coils 2 respectively, a mode selection switch 5 selected by a driver, a main relay SW9 for turning ON and OFF a current flowing to the relay circuit 4, and a foot switch 9 provided for a foot brake 7.
The functions of this brake are explained as follows. When the driver determines that a main brake is under an excessive load because the vehicle is running, for example, on a downward slope, or that the electromagnetic brake alone is sufficient, the driver selects switches SW1 to SW8 of the mode selection switch 5, and pushes the foot brake 7 to turn ON the foot switch 9 anti main relay SW9, and accordingly, the relays RL1 to RL8 of the relay circuit 4 corresponding to the selected switches 5 are turned ON to magnetize the corresponding electromagnetic coils 2.
As a result, the rotor 3 is rotated in magnetic fields produced by the magnetic coils 2, and an eddy current flows in the rotor 3 to produce Joule heat that generates a braking torque for braking the vehicle.
When the conventional electromagnetic brake is used with the main brake, the driver must select the switches SW1 to SW8 of the mode selection switch 5 whenever the driving condition such as running on a downward slope is changed, and this may raise the following problems: switches SW1 to SW4 are turned OFF in response to a change in the driving condition, to reduce the number of active electromagnetic coils 2, a braking torque D.tau. is changed stepwise as indicated by the braking torque characteristic curve of FIG. 2, and as a result, the driver has a feeling of discomfort. and therefore, these coils often reach an operating temperature limit.
Further, according to the prior art, all of the switches SW1 to SW8 may be turned ON and used for a long time, depending on the driving condition, and thus the temperature of the rotor 3 may sometimes become higher than 600.degree. C., depending on an inclination of a road, operating conditions, and load, etc.
As a result, a first problem arises in that the periphery of the brake is heated and the rotary drum 3 is deformed.
When all of the electromagnetic c
REFERENCES:
patent: 3689778 (1972-09-01), Sharp
patent: 3704769 (1972-12-01), Spencer
patent: 3837442 (1974-09-01), Baermann
patent: 4050743 (1977-09-01), Knight
patent: 4131325 (1978-12-01), Bayliss
patent: 4164987 (1979-08-01), Lagarde
patent: 4305485 (1981-12-01), Dubreucq
patent: 4853573 (1989-08-01), Wolcott et al.
patent: 5023499 (1991-06-01), Kuwahara
Akima Hideo
Ishikura Yoshikiyo
Kishi Takaaki
Fujitsu Ltd.
Graham Matthew C.
Tokyo Buhin Kogiyo Co., Ltd.
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