Coil construction

Abstract

A bifilar coil construction is used for isolating radio signals picked up by a motor vehicle window heating element from the power supply circuit for the heating element. The coil construction has two separate windings (9,10) which are arranged bodily alongside each other. In one embodiment there is an inner cylindrical winding (9) within and in contact with an outer cylindrical winding (10), and a two part pot core (15,16) is clamped within and around the windings (9,10).

Description

This application is a continuation of application Ser. No. 08/313,162, filed Jan. 17, 1995, abandoned

BEST MODE OF CARRYING OUT THE INVENTION

The signal separating device shown is for use with a conventional heated rear window of a motor car to enable this to be used as a receiving antenna for a car radio.

The device comprises a housed circuit 1 which is fixed close to the heated window 2 e.g. beneath the rear parcel shelf or within the roof lining.

The housed circuit 1 has five terminals, 3, 4, 5, 6, 7, two of which 3, 4 are connected to the heating element 2 of the window, another two of which 5, 6 are connected to d.c. positive and earth of the car d.c. power supply via the usual dash board switch, and the other of which 7 is connected by a shielded cable to the car radio antenna input circuit.

The housed circuit 1 includes a bifilar coil 8 having two windings 9, 10 of common direction or hand which are interposed respectively between d.c. positive and earth and the two ends of the heating element 2.

The antenna terminal 7 is linked to the heating element 2 between the heating element 2 and the bifilar coil construction 8. Other components for matching, tuning, assistance in isolation, balancing of the signals at the ends of the heating element etc. may be incorporated but are not all shown here.

The bifilar coil construction comprises two separate windings 9, 10 each of say 5 turns of a thick gauge copper wire capable of carrying said 30 amps without overheating and without significant voltage loss due to resistance.

Each winding coil 9, 10 has a bottom turn which terminates in a downwardly bent end 11, 12 projecting freely away from the coil parallel to its axis. Each coil also has a top turn which terminates in a downwardly bent end 13, 14 projecting freely from the coil alongside and spaced from the outersurface of the coil parallel to its axis.

The inner coil 9 has an outer diameter which is very slightly smaller than the inner diameter of the outer coil 10. The end 11 of the inner coil is bent directly downwardly whereas the ends 13, 12, 14 of the inner and outer coil are stepped to one side before being bent downwardly.

The inner coil 9 is fitted within the outer coil 10 so that they are closely in contact with each other. The bottom projecting ends 11, 12 are alongside each other but are spaced apart due to the above mentioned stepping. A similar arrangement applies to the top projecting ends 13, 14.

Due to the fact that the end 11 is bent directly downwards whereas the other ends 12-14 are stepped as described, it will be understood that the coil 9 can be quickly and easily inserted into the coil 10 after winding without any further bending or forming of the ends 11-14.

The coils so far described can be readily formed with a conventional winding machine since it is a single wire which is being wound. In particular, the ends 11, 12, 13, 14 can be readily bent and fed in to (or fed out of) the associated end turn in a particularly simple and accurate manner, and without requiring undue axial distortion or displacement of the end turn, even with the thick gauge wire.

The resulting coil construction 8 has reduced axial bulk due to the radial spacing of the turns of the two windings 9, 10 and due to the above mentioned reduced displacement of the end turns.

The coil construction 8 is accurately shaped and configured and so it can be easily assembled with a conventional pot core, as shown in the drawing.

The pot core is formed in two halves 15, 16 each consisting of an inner hollow cylinder, 17, an outer hollow cylinder 18 and an end plate 19. These cylinders 17, 18 and the end plate 19 are formed integrally in one piece from a ferrous ceramic structure.

There is a gap in the outer cylinder 18 and the end plate 19 forming a radial slot 20, and there is a central hole 21 in the end plate 19.

The core halves 15, 16 are assembled top and bottom around the coil construction with the radial slots 20 offset to receive the projecting ends 11, 12, 13, 14. The halves 15, 16 are clamped in position tightly in contact with each other with a bolt 22 passed through the holes 21 and the inner cylinders 17 and engaging a nut 23.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Claims

1. A signal separating device for use with a window heating element (2) of a motor vehicle, the signal separating device (1) having a first pair of terminals (3,4) for connection to the heating element (2), a second pair of terminals (5,6) for connection to d.c. power supply for the heating element, and an antenna terminal (7) for connection to radio transmitting and/or receiving apparatus, in which the separating device (1) includes a double-wound coil (8) having first and second separate and generally cylindrical coil windings (9,10) wound in the same direction and formed and disposed such that the first coil winding (9) closely fits within the second coil winding (10) with the turns of the first winding (9) being radially inward of the turns of the second winding (10), the said windings having the same number of turns as one another, said heating element (2) being connected in series between said windings.

2. A signal separating device according to claim 1 in which the antenna terminal (7) is connected intermediate the heating element and the double-wound coil.

3. A signal separating device according to claim 1 further comprising circuit components for matching, tuning, assistance in isolation or balancing of signals.

4. A signal separating device according to claim 1 in which each separate coil winding is formed from wire, at least one end portion of which projects axially of the winding.

5. A signal separating device according to claim 4 in which at least one of the said end portions is radially displaced from the coil winding by a radial portion of wire.

6. A signal separating device according to claim 1 further comprising a pot core having two sections (15,16), each section having inner (17) and outer (18) cylindrical parts respectively within and around said double-wound coil (8), wherein said two sections are clamped together tightly in contact with each other by a bolt (22) and nut (23) which extend axially of said coil.

7. A signal separating device according to claim 1 in which said coil windings are capable of carrying a current of 30 A without overheating and without significant voltage loss due to resistance.

8. A signal separating device according to claim 1 wherein said double-wound coil and its first and second coil windings are formed as spiral or helical coils and which are disposed axially one on top of the other, said coils being of common diameter and disposed in contact with each other, thereby resulting in a flat and reduced axial bulk coil construction.

9. A signal separating device according to claim 8 further comprising a pot core and wherein said spiral or helical coils have central apertures to receive a central part of said pot core.

10. A signal separating device according to claim 1 wherein each of said separate coil windings (9,10) includes one bottom turn coil end (11,12) and one top turn coil end (13,14), each of said bottom and top coil ends terminating in a downwardly bent end, said one bottom turn coil end (11) of said first coil winding (9) projecting downwardly and axially away from the said first coil winding inside its outersurface and parallel to its axis, and said one bottom turn coil end (12) of said second coil winding (10) and said top turn coil ends (13,14) projecting freely away from and downwardly alongside the outersurface of their respective coil windings.

11. A signal separating device according to claim 6 wherein each of said separate coil windings (9,10) includes one bottom turn coil end (11,12) and one top turn coil end (13,14), each of said bottom and top coil ends terminating in a downwardly bent end, said one bottom turn coil end (11) of said first coil winding (9) projecting downwardly and axially away from the said first coil winding inside its outersurface and parallel to its axis, and said one bottom turn coil end (12) of said second coil winding (10) and said top turn coil ends (13,14) projecting freely away from and downwardly alongside the outersurface of its respective coil winding.

12. A signal separating device according to claim 11 wherein said bottom and top turn coil ends (11,12,13,14) are received within and extend through offset radial slots (20) of said pot core.

13. A signal separating device according to claim 12 wherein said radial slots (20) are provided within and by said two sections (15,16) of the said pot core.

14. A signal separating device for use with a window heating element (2) of a motor vehicle, the signal separating device (1) having

a first pair of terminals (3,4) for connection to the heating element (2),

a second pair of terminals (5,6) for connection to a d.c. power supply for the heating element and

an antenna terminal (7) for connection to radio transmitting and/or receiving apparatus,

the separating device (1) including a double-wound coil (8) having first and second separate coil windings wherein said double-wound coil and its first and second coil windings are formed as spiral or helical coils and which are disposed axially one on top of the other said coils being of common diameter and disposed in contact with each other thereby resulting in a flat and reduced axial bulk construction.

15. A signal separating device according to claim 14, further comprising a pot core and wherein said spiral or helical coils have central apertures to receive a central part of said pot core.