Coil construction

Details Coil construction Coil construction

1999-11-02

2002-09-10

Wimer, Michael C. (Department: 2821)

Communications: radio wave antennas

Antennas

With ice clearer or preventer

C343S860000

Reissue Patent

active

RE037835

ABSTRACT:

TECHNICAL FIELD
This invention relates to a bifilar coil construction.
BACKGROUND ART
British patents GB 1520030 and GB 1600987 describe signal separating devices which act to isolate the d.c. power supply circuit for the heating element of an electrically heated motor vehicle window from the antenna circuit of a radio receiver or transmitter connected to the heating element, so that the heating element can be used simultaneously for heating purposes and as a radio transmitting or receiving antenna.
The described devices use a bifilar coil for signal separation purposes. The two windings of the coil are connected respectively between opposite ends of the heating element and positive and negative terminals of the d.c. power supply circuit, whereby the coil can present a high blocking impedance to radio signals with a low resistance for d.c. currents. Signal separation can therefore be effected in a particularly convenient and efficient manner.
Conventionally, bifilar coils are manufactured by machine-winding two side-by-side wires together around a former. This results in two windings which are wound in a common direction, which have a common diameter and axial length, and the turns of which lie axially next to each other. For signal separation purposes as mentioned above, the windings are enclosed within a pot core structure (ferrous ceramic structure) with ends of the windings projecting axially downwardly through openings in the structure for connection purposes.
Present trends are towards the use of higher current consumption motor vehicle window heating elements, say 30 amps or more, and there is therefore a requirement for bifilar coils with thicker gauge windings. However, with the abovementioned conventional construction, thicker gauge windings result in increased axial bulk which is undesirable. An axially compact construction is desirable to permit easy mounting at a required position close to the motor vehicle window so as to minimise tuning problems due to lead inductance and capacitance. Also, with the conventional construction, the projecting connection ends of the windings follow a curved or bent path where they feed into the adjacent end turns and, in the case of axially side-by-side thicker gauge wires this adds considerably to the axial bulk and also can be difficult to achieve or control with conventional winding equipment.
An object of the present invention is to provide a signal separating device having a doublewound coil construction which can be easily and conveniently manufactured, and with which axial bulk can be minimised, even with thicker gauge wires.
DISCLOSURE OF THE INVENTION
Thus, and in accordance with one aspect of the present invention there is provided a signal separating device for use with a motor vehicle window heating element, said device having a pair of first terminals for connection to the heating element, a pair of second terminals for connection with the motor vehicle d.c. power supply for the heating element, an antenna terminal for connection to the antenna circuit of motor vehicle radio transmitting and/or
receciving

receiving
apparatus, and a double wound coil having first and second windings of common direction interposed between the pair of first terminals and the pair of second terminals so as to permit passage of d.c. current from the power supply to the heating element whilst blocking passage of radio signals from the heating element to the d.c. power supply, the antenna terminal being connected between the heating element and the double wound coil, the windings of the double wound coil being separately formed windings disposed bodily alongside each other and a ferrous core being provided having inner and outer parts respectively within and around the coil structure, the separate windings of the double wound coil comprising first and second generally cylindrical windings of different diameters whereby the first winding fits closely within the second winding with the turns of the first winding spaced radially inwardly of the turns of the second winding, said first and second windings having a substantially identical number of turns thereto.
The signal separating device may include other components as appropriate for example including capacitors, diodes, chokes, matching circuitry for matching the heating element to the antenna circuit of the radio apparatus, and tuning circuitry to give efficient operation at different frequency bands (am, vhf).
The separate windings of the doublewound coil construction of the invention may comprise two cylindrical (or generally cylindrical) windings which are of slightly different diameters so that the first winding can fit closely within the second winding, the turns of the first winding therefore being spaced radially inwardly of the turns of the second winding.
Thus, and in accordance with a second aspect of the present invention, there is provided a method of manufacturing the signal separating device of the first aspect of the invention wherein a method of manufacturing a signal separating device according to any one of claims
1
to
3
including forming the first winding as a generally cylindrical coil from wire having a transverse dimension of greater than 2 mm, forming the second winding as a separate generally cylindrical coil from the same wire having an internal diameter greater than the external diameter of the coil of the first winding, fitting the first winding within the second winding and placing the double wound coil so formed within a 30 mm pot core having inner and outer parts respectively with and around the coil structure whereby a current carrying capability of between 25 to 35 amps is possible in said windings.
Preferably the said internal and external diameters are closely similar so that the outer surface of the first winding contacts or is in close proximity to the inner surface of the second winding for maximum space saving.
With this method, the windings can be formed easily and conveniently, even with thicker gauge wire, especially because the ends of the windings are fed into the adjacent end turns as single wires whereby bends or curves between the ends and the turns can be readily accommodated. Since the winding turns are radially spaced the axial bulk can be kept to a minimum, and the fact that the said bends or curves of the ends occur in single, rather than twin wires can also assist in this respect.
With inner and outer windings, the overall coil structure is of generally cylindrical form and it is possible (and preferred) to use a conventional core having inner and outer cylindrical parts, respectively within and around the coil structure, joined by integral end plates. The core may be a pot core and may be formed in two sections which are clamped together by an axially extending clamping device such as a nut and bolt. Appropriate slots may be provided for the connection ends.
In one embodiment each winding has final top and bottom turns which terminate in respective bent ends with straight terminal end portions which project alongside the coil in the axial direction of the coil. Preferably, the bottom said terminal end portion projects downwardly freely away from the coil, and the top said terminal end portion projects downwardly freely from the coil alongside and spaced from the outer surface thereof. Preferably also, the terminal end portions are spaced circumferentially from each other.
In a particularly preferred embodiment, at least one of the top and bottom bent ends is stepped sideways so that the top terminal end portions of the two windings are spaced apart from each other, as also are the bottom terminal end portions.
The core may have top and bottom radially extending slots through which the top bent ends and the bottom bent ends respectively project.
Alternatively, the separate windings may comprise two spiral (or helical) windings disposed one on top of the other. This results in a “flat”, or reduced axial bulk, construction and the ends of the windings can be readily separately turned up or down or otherwise bent to form connections w

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