Inductor devices – With closed core interrupted by an air gap
Reexamination Certificate
1999-03-02
2003-01-28
Donovan, Lincoln (Department: 2832)
Inductor devices
With closed core interrupted by an air gap
C336S120000, C336S121000, C336S135000
Reexamination Certificate
active
06512437
ABSTRACT:
TECHNICAL FIELD
This invention relates to an isolation transformer and a transmission control apparatus using the isolation transformer.
BACKGROUND ART
The rotary transformer which is one type of the isolation transformer has been frequently used in electric appliances such as video machines.
In an ordinary transformer, two coils are constructed to be rotatable relative to each other, cores having a high relative magnetic permeability are employed to increase the coupling coefficient of the coils and a gap between the cores (coils) is set to an order of several &mgr;m. If the coils coupling coefficient is very high, self inductance and mutual inductance of the two coils cancel out each other, and therefore the I/O impedance of a transformer can be designed to be small. Therefore, in the ordinary rotary transformer, impedance matching with a load can be carried out easily.
In such a rotary transformer, if the gap between the cores deflects during a relative rotation between two coils, the coupling condition between the coils is affected. Thus, production accuracy of components must be controlled strictly. Specifically in case of use in an environment having a violent vibration, if the absolute value of the gap is small, the coupling condition of the coil may be largely affected by a minute vibration, which is disadvantageous from the viewpoint of production cost.
On the other hand, if a necessity of transmitting a large-current, large-volume electric energy at a high speed occurs when the isolation transformer is used under a low voltage, impedance matching between the coil and load is very important for the isolation transformer. For this purpose, in the isolation transformer, it can be considered to reduce the equivalent relative magnetic permeability of its magnetic circuit by increasing the gap between the cores, to reduce coil inductance by decreasing the number of windings of the coil, and to reduce DC resistance of the coil, as well other measures. However, because energy is transmitted instantaneously, the transmission frequency needs to be set high. In this case, the higher the frequency, the larger the coil impedance becomes.
The above problems can be solved by suppressing a reduction of the coupling condition between the coils even if the gap between the cores of the isolation transformer is enlarged.
On the other hand, as a non-contact type electric energy transmission apparatus, there is a type using the rotary transformer (a kind of isolation transformer). This kind of the transmission apparatus transmits electric energy supplied from a power source to a load via the aforementioned rotary transformer. For example as disclosed in Unexamined Japanese Patent Publication (KOKAI) No. 6-191373, this apparatus is used as an apparatus for instantaneously activating a shot-firing device (load) of an automotive air bag.
The aforementioned shot-firing device is activated by applying a large current of about several A in a short time of, for example, less than 2-30 m second. As the aforementioned electric energy transmission apparatus, specifically, a rotary transformer, it is required that its transmission efficiency is high enough to achieve a large-current electric energy transmission. Further, the isolation transformer is required to have an excellent high frequency characteristic to achieve an instantaneous electric energy transmission, and generally, it is desirable to set the transmission frequency over about 10 kHz.
From this viewpoint, various considerations have been taken on the isolation transformer and recently, a flat opposing type inductive, isolation transformer has been much expected.
The flat opposing type isolation transformer has a structure in which primary and secondary cores provided with primary and secondary coils respectively, mounted in each of annular concave portions formed in their opposing faces so that they have a symmetrical shape with respect to an axis, are arranged symmetrically in terms of plane via a predetermined gap.
In the isolation transformer having such a structure, a factor important for achieving highly efficient electric energy transmission is coupling efficiency between the aforementioned two coils. For this purpose, it is a requirement to make magnetic flux as large as possible, generated in the primary coil interlink with the secondary coil, and, to reduce leakage of the magnetic flux. Therefore, much effort has been taken to produce the aforementioned cores with a high magnetic permeability material and to reduce the aforementioned gap as much as possible.
However, there is a limitation in reduction of the gap between the cores and there are following problems. That is, even if a fine gap is set, it is very difficult to maintain that gap at a high accuracy because of an influence of vibration, generated heat and the like. For example, if this kind of the isolation transformer is incorporated in a vehicle as a rotary transformer, the opposing distance between the stator and rotor largely changes due to vibration, generated heat and the like. Thus, if the change rate is of the same order as the gap width, the coupling condition of the isolation transformer largely changes so that its electric transmission efficiency largely changes. That is, as the gap is reduced, the change in transmission efficiency due to the gap change is increased. Therefore, it is difficult to raise the transmission efficiency high enough and stabilize the transmission efficiency in the isolation transformer.
Further, in the isolation transformer, if the gap is reduced, the effective permeability of a magnetic path (magnetic circuit) formed by the cores becomes substantially the same order as the magnetic permeability of the core itself. However, because in the isolation transformer, the coil inductance is increased, a high voltage is necessary for realizing a large current transmission. However, because a 12-V battery is exclusively used as a power source of the vehicle, a boosting circuit for a large current as disclosed in Unexamined Japanese Patent Publication (KOKAI) No. 6-191373 is necessary. Therefore, there occurs such a disadvantage that the isolation transformer has a higher cost.
Further, in some type of conventional transmission control apparatuses, the rotary transformer (a kind of isolation transformers) is used in a steering portion of a vehicle to ignite its air bag from the column side in a non-contact manner. For example, Unexamined Japanese Patent Publication (KOKAI) No. 8-322166 has disclosed an idea in which power transmission necessary for air bag ignition and other signal transmission are achieved in interactive ways by using a rotary transformer having a single shaft structure.
In case of ignition of the air bag, the air bag needs to be activated by supplying a current of several A for more than several tens m seconds instantaneously since detection of a collision to a shot-firing device having a resistance as low as 1-3&OHgr; under a low voltage (the vehicle battery is exclusively 12 V).
In case of power transmission necessary for ignition of the air bag, to satisfy this requirement, the aforementioned conventional transmission control apparatus supplies a small power gradually to charge a capacitor provided on the shaft side with a necessary electric power. When an ignition of the air bag is instructed, the aforementioned instruction signal is multiplex-transmitted from the column side to the shaft side via the rotary transformer by carrier wave. If the ignition is necessary after a necessity of the ignition is determined, the aforementioned capacitor is discharged to supply a large current necessary for the ignition thereby activating the shot-firing device. A communication signal from the shaft side, for example, a signal of ON/OFF of a horn (klaxon) switch or the like is multiplex-transmitted via the rotary transformer.
Because in the aforementioned transmission control apparatus, when the ignition of the air bag is instructed, the aforementioned instruction signal is transmitted to the secondary side of the rotary transforme
Abe Fumihiko
Jin Dongzhi
Mochizuki Hajime
Nguyen Tuyen T.
The Furukawa Electric Co. Ltd.
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